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<body style="display: inherit; "><div class="head"><p></p><h1 class="title" id="title">JSON-LD 1.0</h1><h2 id="subtitle">A Context-based JSON Serialization for Linking Data</h2><h2 id="unofficial-draft-03-august-2011">Unofficial Draft 03 August 2011</h2><dl><dt>Editors:</dt><dd><a href="http://digitalbazaar.com/">Manu Sporny</a>, <a href="http://digitalbazaar.com/">Digital Bazaar, Inc.</a></dd>
<dd><a href="http://greggkellogg.net/">Gregg Kellogg</a>, Kellogg Associates</dd>
<dt>Authors:</dt><dd><a href="http://webbackplane.com/">Mark Birbeck</a>, <a href="http://webbackplane.com/">Backplane Ltd.</a></dd>
<dd><a href="http://digitalbazaar.com/">Manu Sporny</a>, <a href="http://digitalbazaar.com/">Digital Bazaar, Inc.</a></dd>
</dl><p class="copyright">This document is licensed under a <a class="subfoot" href="http://creativecommons.org/licenses/by/3.0/" rel="license">Creative Commons Attribution 3.0 License</a>.</p><hr /></div>
<div id="abstract" class="introductory section"><h2>Abstract</h2>
<p>
JSON [<cite><a class="bibref" rel="biblioentry" href="#bib-RFC4627">RFC4627</a></cite>] has proven to be a highly useful object serialization and 
messaging format. In an attempt to harmonize the representation of Linked Data 
in JSON, this specification outlines a common JSON representation format for 
expressing directed graphs; mixing both Linked Data and non-Linked Data in 
a single document. 
</p>
</div><div id="sotd" class="introductory section"><h2>Status of This Document</h2><p>This document is merely a public working draft of a potential specification. It has no official standing of any kind and does not represent the support or consensus of any standards organisation.</p>
<p>This document is an experimental work in progress.</p>

<!--  <p>
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</div><div id="toc" class="section"><h2 class="introductory">Table of Contents</h2><ul class="toc"><li class="tocline"><a href="#introduction" class="tocxref"><span class="secno">1. </span>Introduction</a><ul class="toc"><li class="tocline"><a href="#how-to-read-this-document" class="tocxref"><span class="secno">1.1 </span>How to Read this Document</a></li><li class="tocline"><a href="#contributing" class="tocxref"><span class="secno">1.2 </span>Contributing</a></li></ul></li><li class="tocline"><a href="#design" class="tocxref"><span class="secno">2. </span>Design</a><ul class="toc"><li class="tocline"><a href="#goals-and-rationale" class="tocxref"><span class="secno">2.1 </span>Goals and Rationale</a></li><li class="tocline"><a href="#linked-data" class="tocxref"><span class="secno">2.2 </span>Linked Data</a></li><li class="tocline"><a href="#linking-data" class="tocxref"><span class="secno">2.3 </span>Linking Data</a></li><li class="tocline"><a href="#the-context" class="tocxref"><span class="secno">2.4 </span>The Context</a><ul class="toc"><li class="tocline"><a href="#inside-a-context" class="tocxref"><span class="secno">2.4.1 </span>Inside a Context</a></li></ul></li><li class="tocline"><a href="#from-json-to-json-ld" class="tocxref"><span class="secno">2.5 </span>From JSON to JSON-LD</a></li></ul></li><li class="tocline"><a href="#basic-concepts" class="tocxref"><span class="secno">3. </span>Basic Concepts</a><ul class="toc"><li class="tocline"><a href="#iris" class="tocxref"><span class="secno">3.1 </span>IRIs</a></li><li class="tocline"><a href="#identifying-the-subject" class="tocxref"><span class="secno">3.2 </span>Identifying the Subject</a></li><li class="tocline"><a href="#specifying-the-type" class="tocxref"><span class="secno">3.3 </span>Specifying the Type</a></li><li class="tocline"><a href="#strings" class="tocxref"><span class="secno">3.4 </span>Strings</a></li><li class="tocline"><a href="#string-internationalization" class="tocxref"><span class="secno">3.5 </span>String Internationalization</a></li><li class="tocline"><a href="#datatypes" class="tocxref"><span class="secno">3.6 </span>Datatypes</a></li><li class="tocline"><a href="#multiple-objects-for-a-single-property" class="tocxref"><span class="secno">3.7 </span>Multiple Objects for a Single Property</a></li><li class="tocline"><a href="#multiple-typed-literals-for-a-single-property" class="tocxref"><span class="secno">3.8 </span>Multiple Typed Literals for a Single Property</a></li><li class="tocline"><a href="#compaction" class="tocxref"><span class="secno">3.9 </span>Compaction</a></li><li class="tocline"><a href="#expansion" class="tocxref"><span class="secno">3.10 </span>Expansion</a></li><li class="tocline"><a href="#framing" class="tocxref"><span class="secno">3.11 </span>Framing</a></li></ul></li><li class="tocline"><a href="#advanced-concepts" class="tocxref"><span class="secno">4. </span>Advanced Concepts</a><ul class="toc"><li class="tocline"><a href="#automatic-typing" class="tocxref"><span class="secno">4.1 </span>Automatic Typing</a></li><li class="tocline"><a href="#type-coercion" class="tocxref"><span class="secno">4.2 </span>Type Coercion</a></li><li class="tocline"><a href="#chaining" class="tocxref"><span class="secno">4.3 </span>Chaining</a></li><li class="tocline"><a href="#identifying-unlabeled-nodes" class="tocxref"><span class="secno">4.4 </span>Identifying Unlabeled Nodes</a></li><li class="tocline"><a href="#overriding-keywords" class="tocxref"><span class="secno">4.5 </span>Overriding Keywords</a></li><li class="tocline"><a href="#normalization" class="tocxref"><span class="secno">4.6 </span>Normalization</a></li></ul></li><li class="tocline"><a href="#algorithms" class="tocxref"><span class="secno">5. </span>Algorithms</a><ul class="toc"><li class="tocline"><a href="#compaction-1" class="tocxref"><span class="secno">5.1 </span>Compaction</a></li><li class="tocline"><a href="#expansion-1" class="tocxref"><span class="secno">5.2 </span>Expansion</a></li><li class="tocline"><a href="#framing-1" class="tocxref"><span class="secno">5.3 </span>Framing</a></li><li class="tocline"><a href="#normalization-1" class="tocxref"><span class="secno">5.4 </span>Normalization</a></li><li class="tocline"><a href="#rdf-conversion" class="tocxref"><span class="secno">5.5 </span>RDF Conversion</a><ul class="toc"><li class="tocline"><a href="#overview" class="tocxref"><span class="secno">5.5.1 </span>Overview</a></li><li class="tocline"><a href="#processing-algorithm-terms" class="tocxref"><span class="secno">5.5.2 </span>Processing Algorithm Terms</a></li><li class="tocline"><a href="#processing-tokens-and-keywords" class="tocxref"><span class="secno">5.5.3 </span>Processing Tokens and Keywords</a></li><li class="tocline"><a href="#context-1" class="tocxref"><span class="secno">5.5.4 </span>Context</a></li><li class="tocline"><a href="#iri-processing" class="tocxref"><span class="secno">5.5.5 </span>IRI Processing</a></li><li class="tocline"><a href="#sequence" class="tocxref"><span class="secno">5.5.6 </span>Sequence</a></li></ul></li></ul></li><li class="tocline"><a href="#experimental-concepts" class="tocxref"><span class="secno">6. </span>Experimental Concepts</a><ul class="toc"><li class="tocline"><a href="#disjoint-graphs" class="tocxref"><span class="secno">6.1 </span>Disjoint Graphs</a></li><li class="tocline"><a href="#the-json-ld-api" class="tocxref"><span class="secno">6.2 </span>The JSON-LD API</a><ul class="toc"><li class="tocline"><a href="#methods" class="tocxref"><span class="secno">6.2.1 </span>Methods</a></li><li class="tocline"><a href="#methods-1" class="tocxref"><span class="secno">6.2.2 </span>Methods</a></li><li class="tocline"><a href="#methods-2" class="tocxref"><span class="secno">6.2.3 </span>Methods</a></li></ul></li></ul></li><li class="tocline"><a href="#markup-examples" class="tocxref"><span class="secno">A. </span>Markup Examples</a><ul class="toc"><li class="tocline"><a href="#rdfa" class="tocxref"><span class="secno">A.1 </span>RDFa</a></li><li class="tocline"><a href="#microformats" class="tocxref"><span class="secno">A.2 </span>Microformats</a></li><li class="tocline"><a href="#microdata" class="tocxref"><span class="secno">A.3 </span>Microdata</a></li><li class="tocline"><a href="#mashing-up-vocabularies" class="tocxref"><span class="secno">A.4 </span>Mashing Up Vocabularies</a></li><li class="tocline"><a href="#acknowledgements" class="tocxref"><span class="secno">A.5 </span>Acknowledgements</a></li></ul></li><li class="tocline"><a href="#references" class="tocxref"><span class="secno">B. </span>References</a><ul class="toc"><li class="tocline"><a href="#normative-references" class="tocxref"><span class="secno">B.1 </span>Normative references</a></li><li class="tocline"><a href="#informative-references" class="tocxref"><span class="secno">B.2 </span>Informative references</a></li></ul></li></ul></div>



<div id="introduction" class="section">

<!-- OddPage -->
<h2><span class="secno">1. </span>Introduction</h2>

<p>
JSON, as specified in [<cite><a class="bibref" rel="biblioentry" href="#bib-RFC4627">RFC4627</a></cite>], is a simple language for representing 
data on the Web. Linked Data is a technique for describing content across 
different 
documents or Web sites. Web resources are described using <a class="tref internalDFN" title="IRI" href="#dfn-iri">IRI</a>s, 
and typically are dereferencable entities that may be used to find more 
information, creating a "Web of Knowledge". JSON-LD is intended to be a simple 
publishing method for expressing not only Linked Data in JSON, but for adding
semantics to existing JSON.
</p>

<p>
JSON-LD is designed as a light-weight syntax that can be used to express 
Linked Data. It is primarily intended to be a way to express Linked Data 
in Javascript and other Web-based programming environments. It is also 
useful when building interoperable Web Services and when storing Linked 
Data in JSON-based document storage engines. It is practical and designed 
to be as simple as possible, utilizing the large number of JSON parsers 
and existing code that is in use today. It is designed to be able to 
express key-value pairs, RDF data, RDFa [<cite><a class="bibref" rel="biblioentry" href="#bib-RDFA-CORE">RDFA-CORE</a></cite>] data, Microformats 
[<cite><a class="bibref" rel="biblioentry" href="#bib-MICROFORMATS">MICROFORMATS</a></cite>] data, and Microdata [<cite><a class="bibref" rel="biblioentry" href="#bib-MICRODATA">MICRODATA</a></cite>]. That is, it supports 
every major Web-based structured data model in use today. 
</p>

<p>
The syntax does not require many applications to change their JSON, but 
easily add meaning by adding context in a way that is either in-band or 
out-of-band. The syntax is designed to not disturb already deployed systems 
running on JSON, but provide a smooth migration path from JSON to JSON with 
added semantics. Finally, the format is intended to be fast to parse, fast to 
generate, stream-based and document-based processing compatible, and require
a very small memory footprint in order to operate.
</p>

<div id="how-to-read-this-document" class="section">
<h3><span class="secno">1.1 </span>How to Read this Document</h3>

<p>
This document is a detailed specification for a serialization of JSON for Linked
data. The document is primarily intended for the following audiences:
</p>

<ul>
  <li>Web developers that want to understand the design decisions and 
  language syntax for JSON-LD.</li>
  <li>Software developers that want to encode Microformats, RDFa, or Microdata 
  in a way that is cross-language compatible via JSON.</li>
  <li>Software developers that want to implement processors and APIs for 
  JSON-LD.</li>
</ul>

<p>
To understand the basics in this specification you must first be familiar with 
JSON, which is detailed in [<cite><a class="bibref" rel="biblioentry" href="#bib-RFC4627">RFC4627</a></cite>]. To understand the API and how it is
intended to operate  in a programming environment, it is useful to have working 
knowledge of the JavaScript programming language [<cite><a class="bibref" rel="biblioentry" href="#bib-ECMA-262">ECMA-262</a></cite>] and 
WebIDL [<cite><a class="bibref" rel="biblioentry" href="#bib-WEBIDL">WEBIDL</a></cite>]. To understand how JSON-LD maps to RDF, it is helpful to be 
familiar with the basic RDF concepts [<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-CONCEPTS">RDF-CONCEPTS</a></cite>].</p>
</div>

<div id="contributing" class="section">
<h3><span class="secno">1.2 </span>Contributing</h3>

<p>There are a number of ways that one may participate in the development of
this specification:</p>

<ul>
<li>Technical discussion typically occurs on the public mailing list:
<a href="http://lists.w3.org/Archives/Public/public-linked-json/">public-linked-json@w3.org</a>
</li>

<li><a href="http://json-ld.org/minutes/">Public teleconferences</a> are held 
on Tuesdays at 1500UTC on the second and fourth week of each month.
</li>

<li>Specification bugs and issues should be reported in the 
<a href="https://github.com/json-ld/json-ld.org/issues">issue tracker</a>.</li>

<li><a href="https://github.com/json-ld/json-ld.org/tree/main/spec">Source code</a> for the 
specification can be found on Github.</li>

<li>The <a href="http://webchat.freenode.net/?channels=#json-ld">#json-ld</a> 
IRC channel is available for real-time discussion on irc.freenode.net.</li>
</ul>

</div>

</div>

<div id="design" class="section">

<!-- OddPage -->
<h2><span class="secno">2. </span>Design</h2>

<p>The following section outlines the design goals and rationale behind the 
JSON-LD markup language.
</p>

<div id="goals-and-rationale" class="section">
<h3><span class="secno">2.1 </span>Goals and Rationale</h3>

<p>
A number of design considerations were explored during the creation of this 
markup language:
</p>

<dl>
 <dt>Simplicity</dt>
 <dd>Developers need only know JSON and three keywords to use the basic 
 functionality in JSON-LD. No extra processors or software libraries are
 necessary to use JSON-LD in its most basic form. The language attempts to
 ensure that developers have an easy learning curve.</dd>
 <dt>Compatibility</dt>
 <dd>The JSON-LD markup must be 100% compatible with JSON. This ensures that
 all of the standard JSON libraries work seamlessly with JSON-LD documents.</dd>
 <dt>Expressiveness</dt>
 <dd>The syntax must be able to express directed graphs, which have been proven
 to be able to simply express almost every real world data model.</dd>
 <dt>Terseness</dt>
 <dd>The JSON-LD syntax must be very terse and human readable, requiring as
 little as possible from the developer.</dd>
 <dt>Pragmatism</dt>
 <dd>Mixing the expression of pure Linked Data with data that is not
 linked was an approach that was driven by pragmatism. JSON-LD attempts to be
 more practical than theoretical in its approach to Linked Data.</dd>
 <dt>Zero Edits, most of the time</dt>
 <dd>JSON-LD provides a mechanism that allows developers to specify 
 context in a way that is out-of-band. This allows organizations that have
 already deployed large JSON-based infrastructure to add meaning to their
 JSON in a way that is not disruptive to their day-to-day operations and is
 transparent to their current customers. At times, mapping JSON to 
 a graph representation can become difficult. In these instances, rather than 
 having JSON-LD support esoteric markup, we chose not to support the use case 
 and support a simplified syntax instead. So, while Zero Edits was a goal,
 it was not always possible without adding great complexity to the language.
 </dd>
 <dt>Streaming</dt>
 <dd>The format supports both document-based and stream-based processing.</dd>
</dl>
</div>

<div id="linked-data" class="section">
<h3><span class="secno">2.2 </span>Linked Data</h3>
<p>
The following definition for <a class="tref internalDFN" title="Linked_Data" href="#dfn-linked_data">Linked Data</a> is the one that will 
be used for this specification.
</p>
<ol>
 <li><dfn title="Linked_Data" id="dfn-linked_data">Linked Data</dfn> is a set of documents, each containing a 
   representation of a linked data graph.</li>
 <li>A <dfn title="linked_data_graph" id="dfn-linked_data_graph">linked data graph</dfn> is a labeled directed graph, where nodes 
   are <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a>s or <a class="tref internalDFN" title="object" href="#dfn-object">object</a>s, and edges are 
   properties.</li>
 <li>A <dfn title="subject" id="dfn-subject">subject</dfn> is any node in a <a class="tref internalDFN" title="linked_data_graph" href="#dfn-linked_data_graph">linked data graph</a> 
   with at least one outgoing edge.</li>
 <li>A <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a> <em class="rfc2119" title="should">should</em> be labeled with a IRI.</li>
 <li>A <dfn title="property" id="dfn-property">property</dfn> is an edge of the <a class="tref internalDFN" title="linked_data_graph" href="#dfn-linked_data_graph">linked data graph</a>
   .</li>
 <li>A <a class="tref internalDFN" title="property" href="#dfn-property">property</a> <em class="rfc2119" title="must">must</em> be labeled with an IRI.</li>
 <li>An <dfn title="object" id="dfn-object">object</dfn> is a node in a <a class="tref internalDFN" title="linked_data_graph" href="#dfn-linked_data_graph">linked data graph</a> with 
   at least one incoming edge.</li>
 <li>An <a class="tref internalDFN" title="object" href="#dfn-object">object</a> <em class="rfc2119" title="may">may</em> be labeled with an IRI.</li>
 <li>An IRI that is a label in a <a class="tref internalDFN" title="linked_data_graph" href="#dfn-linked_data_graph">linked data graph</a> <em class="rfc2119" title="should">should</em> be 
   dereferencable to a <a class="tref internalDFN" title="Linked_Data" href="#dfn-linked_data">Linked Data</a> document describing the 
   labeled <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a>, <a class="tref internalDFN" title="object" href="#dfn-object">object</a> or <a class="tref internalDFN" title="property" href="#dfn-property">property</a>
   .</li>
 <li>A <dfn title="literal" id="dfn-literal">literal</dfn> is an <a class="tref internalDFN" title="object" href="#dfn-object">object</a> with a label that is not 
 an IRI</li>
</ol>

<p>
Note that the definition for <a class="tref internalDFN" title="Linked_Data" href="#dfn-linked_data">Linked Data</a> above is silent on the 
topic of unlabeled nodes. Unlabeled nodes are not considered 
<a class="tref internalDFN" title="Linked_Data" href="#dfn-linked_data">Linked Data</a>. However, this specification allows for the expression
of unlabled nodes, as most graph-based data sets on the Web contain a number 
of associated nodes that are not named and thus are not directly 
de-referenceable.
</p>
</div>

<div id="linking-data" class="section">
<h3><span class="secno">2.3 </span>Linking Data</h3>

<p>
An Internationalized Resource Identifier 
(<dfn title="IRI" id="dfn-iri"><abbr title="Internationalized Resource Identifier">IRI</abbr></dfn>),
as described in [<cite><a class="bibref" rel="biblioentry" href="#bib-RFC3987">RFC3987</a></cite>], is a mechanism for representing unique 
identifiers on the web. In <a class="tref internalDFN" title="Linked_Data" href="#dfn-linked_data">Linked Data</a>, an IRI is commonly 
used for expressing a <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a>, a <a class="tref internalDFN" title="property" href="#dfn-property">property</a> or an 
<a class="tref internalDFN" title="object" href="#dfn-object">object</a>.
</p>

<p>JSON-LD defines a mechanism to map JSON values to IRIs. This does not mean 
that JSON-LD requires every key or value to be an IRI, but rather ensures that
keys and values can be mapped to IRIs if the developer so desires to transform
their data into Linked Data. There are a few techniques that can ensure 
that developers will generate good Linked Data for the Web. JSON-LD 
formalizes those techniques.
</p>

<p>We will be using the following JSON markup as the example for the
rest of this section:
</p>

<pre class="example">
{
  "name": "Manu Sporny",
  "homepage": "http://manu.sporny.org/"
  "avatar": "http://twitter.com/account/profile_image/manusporny"
}</pre>
</div>

<div id="the-context" class="section">
<h3><span class="secno">2.4 </span>The Context</h3>

<p>In JSON-LD, a context is used to allow developers to map <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s 
to <a class="tref internalDFN" title="IRI" href="#dfn-iri">IRI</a>s. A <dfn title="term" id="dfn-term">term</dfn> is a short word that <em class="rfc2119" title="may">may</em> be expanded
to an <a class="tref internalDFN" title="IRI" href="#dfn-iri">IRI</a>. The semantic web, just like the document-based 
web, uses IRIs for unambiguous identification. The idea is that these 
<a class="tref internalDFN" title="term" href="#dfn-term">term</a>s mean something that may be of use to other developers.
For example, the term <code>name</code> may map directly to the IRI 
<code>http://xmlns.com/foaf/0.1/name</code>. This allows JSON-LD documents to 
be constructed using the common JSON practice of simple name/value pairs while
ensuring that the data is useful outside of the database or page in which it
resides.
</p>

<p>These Linked Data <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s are typically collected in a context and
then used by adding a single line to the JSON markup above:</p>

<pre class="example">
{
  <span class="diff">"@context": "http://example.org/json-ld-contexts/person",</span>
  "name": "Manu Sporny",
  "homepage": "http://manu.sporny.org/"
  "avatar": "http://twitter.com/account/profile_image/manusporny"
}</pre>

<p>The addition above transforms the previous JSON document into a JSON document
with added semantics because the <code>@context</code> specifies how the
<strong>name</strong>, <strong>homepage</strong>, and <strong>avatar</strong> 
terms map to IRIs. 
Mapping those keys to IRIs gives the data global context. If two 
developers use the same IRI to describe a property, they are more than likely
expressing the same concept. This allows both developers to re-use each others
data without having to agree to how their data will inter-operate on a 
site-by-site basis.</p>

<p>
The semantic web uses a special type of document called a 
<em>Web Vocabulary</em> to define <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s. A context is a type of
Web vocabulary.
Typically, these Web Vocabulary documents have <a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a>es associated
with them and contain a number of <a class="tref internalDFN" title="term" href="#dfn-term">term</a> declarations. A
<dfn title="prefix" id="dfn-prefix">prefix</dfn>, like a <a class="tref internalDFN" title="term" href="#dfn-term">term</a>, is a short word that expands
to a Web Vocabulary IRI. <a class="tref internalDFN" title="Prefix" href="#dfn-prefix">Prefix</a>es are helpful when a developer
wants to mix multiple vocabularies together in a context, but does not want
to go to the trouble of defining every single term in every single vocabulary.
Some Web Vocabularies may have 10-20 terms defined. If a developer wants to use 
3-4 different vocabularies, the number of terms that 
would have to be declared in a single context would become quite large. To 
reduce the number of different terms that must be defined, JSON-LD also allows 
prefixes to be used to compact IRIs.
</p><p>

</p><p>For example, the IRI <code>http://xmlns.com/foaf/0.1/</code> 
specifies a Web Vocabulary which may be represented using the
<code>foaf</code> <a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a>. The <code>foaf</code> Web Vocabulary
contains a term called <strong>name</strong>. If you join the 
<code>foaf</code> <a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a> with the <strong>name</strong> suffix, 
you can build a compact IRI that will expand out into an absolute IRI for the
<code>http://xmlns.com/foaf/0.1/name</code> vocabulary term.
That is, the compact IRI, or short-form, is <code>foaf:name</code> and the 
expanded-form is <code>http://xmlns.com/foaf/0.1/name</code>. This vocabulary 
term is used to specify a person's name.
</p>

<p>Developers, and machines, are able to use this IRI (plugging it
directly into a web browser, for instance) to go to the term and get a 
definition of what the term means. Much like we can use WordNet today to 
see the 
<a href="http://wordnetweb.princeton.edu/perl/webwn?s=definition">definition</a>
of words in the English language. Developers and machines need the same sort of 
dictionary of terms. IRIs provide a way to ensure that these terms
are unambiguous.
</p>

<p>The context provides a collection of vocabulary <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s and 
<a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a>es that can be used to expand JSON keys and values into
<a class="tref internalDFN" title="IRI" href="#dfn-iri">IRI</a>s.</p>

<div id="inside-a-context" class="section">
<h4><span class="secno">2.4.1 </span>Inside a Context</h4>

<p>In the previous section, the developer used the <code>@context</code>
keyword to pull in an external context. That context document, if 
de-referenced, would look something like this:</p>

<pre class="example">
{
    "name": "http://xmlns.com/foaf/0.1/name",
    "homepage": "http://xmlns.com/foaf/0.1/homepage"
    "avatar": "http://xmlns.com/foaf/0.1/avatar"
}</pre>

<p>A JSON-LD context document is a simple mapping from <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s and
<a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a>es to IRIs. Contexts may also contain datatype information
for certain <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s as well as other processing instructions for
the JSON-LD processor.
</p>

<p>Contexts may be specified in-line. This ensures that JSON-LD documents
can be processed when a JSON-LD processor does not have access to the Web.</p>

<p>
JSON-LD strives to ensure that developers don't have to change the JSON
that is going into and being returned from their Web applications. This means
that developers can also specify a context for JSON data in an out-of-band
fashion via the API. The API is described later in this document. A JSON-LD 
aware Web Service <em class="rfc2119" title="may">may</em> also define a context that will be pre-loaded for all
calls to the service. This allows services that have previously been publishing
and receiving JSON data to accept JSON-LD data without requiring client 
software to change.
</p>

</div>

</div>

<div id="from-json-to-json-ld" class="section">
<h3><span class="secno">2.5 </span>From JSON to JSON-LD</h3>

<p>If a set of terms such as, <strong>name</strong>, <strong>homepage</strong>, 
and <strong>avatar</strong>,
are defined in a context, and that context is used to resolve the
names in JSON objects, machines are able to automatically expand the terms to 
something meaningful and unambiguous, like this:</p>

<pre class="example">
{
  "<span class="diff">http://xmlns.com/foaf/0.1/name</span>": "Manu Sporny",
  "<span class="diff">http://xmlns.com/foaf/0.1/homepage</span>": "http://manu.sporny.org"
  "<span class="diff">http://rdfs.org/sioc/ns#avatar</span>": "http://twitter.com/account/profile_image/manusporny"
}</pre>

<p>Doing this allows JSON to be unambiguously machine-readable without
requiring developers that use JSON to drastically change their workflow.</p>
</div>

</div>



<div id="basic-concepts" class="section">

<!-- OddPage -->
<h2><span class="secno">3. </span>Basic Concepts</h2>

<p>JSON-LD is designed to ensure that Linked Data concepts can be marked 
up in a way that is simple to understand and author by Web developers. In many
cases, regular JSON markup can become Linked Data with the simple addition
of a context. As more JSON-LD features are used, more semantics are added
to the JSON markup.</p>

<div id="iris" class="section">
<h3><span class="secno">3.1 </span>IRIs</h3>

<p>Expressing IRIs are fundamental to Linked Data as that is how most 
<a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a>s and many <a class="tref internalDFN" title="object" href="#dfn-object">object</a> are named. IRIs can be 
expressed in a variety of different ways in JSON-LD.</p>

<ol>
  <li>In general, <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s in the key position in 
    an associative array that have a mapping to an IRI in the context are
    expanded to an IRI by JSON-LD processors. There are special rules for 
    processing keys in <code>@context</code> and when dealing with keys that 
    start with the <code>@</code> character.</li>
  <li>An IRI is generated for the value specified using <code>@subject</code>, 
    if it is a string.</li>
  <li>An IRI is generated for the value specified using <code>@type</code>.</li>
  <li>An IRI is generated for the value specified using the <code>@iri</code> 
    keyword.</li>
  <li>An IRI is generated when there are <code>@coerce</code> rules in 
    effect for a key named <code>@iri</code>.</li>
</ol>

<p>IRIs can be expressed directly in the key position like so:
</p>

<pre class="example">
{
...
  "<span class="diff">http://xmlns.com/foaf/0.1/name</span>": "Manu Sporny",
...
}</pre>

<p>In the example above, the key 
<code>http://xmlns.com/foaf/0.1/name</code> is interpreted as an IRI, as 
opposed to being interpreted as a string..</p>

<p>Term expansion occurs for IRIs if a term is defined within the 
<a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a>:</p>

<pre class="example">
{
  "<span class="diff">@context</span>": {"<span class="diff">name</span>": "<span class="diff">http://xmlns.com/foaf/0.1/name</span>"},
...
  "<span class="diff">name</span>": "Manu Sporny",
...
}</pre>

<p><a class="tref internalDFN" title="Prefix" href="#dfn-prefix">Prefix</a>es are expanded when used in keys:</p>

<pre class="example">
{
  "<span class="diff">@context</span>": {"<span class="diff">foaf</span>": "<span class="diff">http://xmlns.com/foaf/0.1/</span>"},
...
  "<span class="diff">foaf:name</span>": "Manu Sporny",
...
}</pre>

<p><code>foaf:name</code> above will automatically expand out to the IRI
<code>http://xmlns.com/foaf/0.1/name</code>.</p>

<p>An IRI is generated when a value is associated with a key using 
the <code>@iri</code> keyword:</p>

<pre class="example">
{
...
  "foaf:homepage": { "<span class="diff">@iri</span>": "http://manu.sporny.org" }
...
}</pre>

<p>If type coercion rules are specified in the <code>@context</code> for
a particular vocabulary term, an IRI is generated:</p>

<pre class="example">
{<span class="diff">
  "@context": 
  { 
    "@coerce": 
    {
      "@iri": "foaf:homepage"
    }
  }</span>
...
  "foaf:homepage": "http://manu.sporny.org/",
...
}</pre>

<p>Even though the value <code>http://manu.sporny.org/</code> is a string,
the type coercion rules will transform the value into an IRI when processed
by a JSON-LD Processor</p>

</div>

<div id="identifying-the-subject" class="section">
<h3><span class="secno">3.2 </span>Identifying the Subject</h3>

<p>A subject is declared using the <code>@subject</code> key. The subject is the
first piece of information needed by the JSON-LD processor in order to
create the (subject, property, object) tuple, also known as a triple.</p>

<pre class="example">
{
...
  "<span class="diff">@subject</span>": "<span class="diff">http://example.org/people#joebob</span>",
...
}</pre>

<p>The example above would set the subject to the IRI 
<code>http://example.org/people#joebob</code>.
</p>

</div>

<div id="specifying-the-type" class="section">
<h3><span class="secno">3.3 </span>Specifying the Type</h3>

<p>The type of a particular subject can be specified using the 
<code>@type</code> key. Specifying the type in this way will generate a 
triple of the form (subject, type, type-url).</p>

<pre class="example">
{
...
  "@subject": "http://example.org/people#joebob",
  "<span class="diff">@type</span>": "<span class="diff">http://xmlns.com/foaf/0.1/Person</span>",
...
}</pre>

<p>The example above would generate the following triple if the JSON-LD 
document is mapped to RDF (in N-Triples notation):</p>

<pre class="example">
&lt;http://example.org/people#joebob&gt; 
   &lt;http://www.w3.org/1999/02/22-rdf-syntax-ns#type&gt;
      &lt;http://xmlns.com/foaf/0.1/Person&gt; .</pre>

</div>

<div id="strings" class="section">
<h3><span class="secno">3.4 </span>Strings</h3>

<p>Regular text strings, also refered to as <dfn title="plain_literal" id="dfn-plain_literal">plain literal</dfn>s, are 
easily expressed using regular JSON strings.</p>

<pre class="example">
{
...
  "foaf:name": "<span class="diff">Mark Birbeck</span>",
...
}</pre>

</div>

<div id="string-internationalization" class="section">
<h3><span class="secno">3.5 </span>String Internationalization</h3>

<p>JSON-LD makes an assumption that strings with associated language encoding 
information are not very common when used in JavaScript and Web Services. 
Thus, it takes a little more effort to express strings with associated 
language information.</p>

<pre class="example">
{
...
  "foaf:name": <span class="diff">
  {
    "@literal": "花澄",
    "@language": "ja"
  }</span>
...
}</pre>

<p>The example above would generate a <a class="tref internalDFN" title="plain_literal" href="#dfn-plain_literal">plain literal</a> for 
<em>花澄</em> and associate the <code>ja</code> language code with the triple 
that is generated. Languages <em class="rfc2119" title="must">must</em> be expressed in [<cite><a class="bibref" rel="biblioentry" href="#bib-BCP47">BCP47</a></cite>] format.</p>

</div>

<div id="datatypes" class="section">
<h3><span class="secno">3.6 </span>Datatypes</h3>

<p>
  A value with an associated datatype, also known as a 
  <dfn title="typed_literal" id="dfn-typed_literal">typed literal</dfn>, is indicated by associating a literal with
  an IRI which indicates the typed literal's datatype. Typed literals may be 
  expressed in JSON-LD in three ways:
</p>

<ol>
  <li>By utilizing the <code>@coerce</code> keyword.</li>
  <li>By utilizing the expanded form for specifying objects.</li>
  <li>By using a native JSON datatype.</li>
</ol>

<p>The first example uses the <code>@coerce</code> keyword to express a
typed literal:</p>

<pre class="example">
{<span class="diff">
  "@context": 
  { 
    "xsd": "http://www.w3.org/2001/XMLSchema#"
    "@coerce": 
    {
      "xsd:dateTime": "dc:modified"
    }
  }</span>
...
  "dc:modified": "2010-05-29T14:17:39+02:00",
...
}</pre>

<p>The second example uses the expanded form for specifying objects:</p>

<pre class="example">
{
...
  "dc:modified": <span class="diff">
  {
    "@literal": "2010-05-29T14:17:39+02:00",
    "@datatype": "xsd:dateTime"
  }</span>
...
}</pre>

<p>Both examples above would generate an object with the literal value of
<code>2010-05-29T14:17:39+02:00</code> and the datatype of
<code>http://www.w3.org/2001/XMLSchema#dateTime</code>.</p>

<p>The third example uses a built-in native JSON type, a number, to 
express a datatype:</p>

<pre class="example">
{
...
  "@subject": "http://example.org/people#joebob",
  "foaf:age": <span class="diff">31</span>
...
}</pre>
d
<p>The example above would generate the following triple:</p>

<pre class="example">
&lt;http://example.org/people#joebob&gt; 
   &lt;http://xmlns.com/foaf/0.1/age&gt; 
      "31"^^&lt;http://www.w3.org/2001/XMLSchema#integer&gt; .</pre>

</div>

<div id="multiple-objects-for-a-single-property" class="section">
<h3><span class="secno">3.7 </span>Multiple Objects for a Single Property</h3>

<p>A JSON-LD author can express multiple triples in a compact way by using
arrays. If a subject has multiple values for the same property, the author
<em class="rfc2119" title="may">may</em> express each property as an array.</p>

<pre class="example">
{
...
  "@": "http://example.org/people#joebob",
  "foaf:nick": <span class="diff">["joe", "bob", "jaybee"]</span>,
...
}</pre>

<p>The markup shown above would generate the following triples:</p>

<pre class="example">
&lt;http://example.org/people#joebob&gt; 
   &lt;http://xmlns.com/foaf/0.1/nick&gt;
      "joe" .
&lt;http://example.org/people#joebob&gt; 
   &lt;http://xmlns.com/foaf/0.1/nick&gt;
      "bob" .
&lt;http://example.org/people#joebob&gt; 
   &lt;http://xmlns.com/foaf/0.1/nick&gt;
      "jaybee" .</pre>

</div>

<div id="multiple-typed-literals-for-a-single-property" class="section">
<h3><span class="secno">3.8 </span>Multiple Typed Literals for a Single Property</h3>

<p>Multiple <a class="tref internalDFN" title="typed_literal" href="#dfn-typed_literal">typed literal</a>s may also be expressed using the expanded
form for objects:</p>

<pre class="example">
{
...
  "@": "http://example.org/articles/8",
  "dcterms:modified": <span class="diff">
  [
    {
      "@literal": "2010-05-29T14:17:39+02:00",
      "@datatype": "xsd:dateTime"
    },
    {
      "@literal": "2010-05-30T09:21:28-04:00",
      "@datatype": "xsd:dateTime"
    }
  ]</span>
...
}</pre>

<p>The markup shown above would generate the following triples:</p>

<pre class="example">
&lt;http://example.org/articles/8&gt; 
   &lt;http://purl.org/dc/terms/modified&gt;
      "2010-05-29T14:17:39+02:00"^^http://www.w3.org/2001/XMLSchema#dateTime .
&lt;http://example.org/articles/8&gt; 
   &lt;http://purl.org/dc/terms/modified&gt;
      "2010-05-30T09:21:28-04:00"^^http://www.w3.org/2001/XMLSchema#dateTime .</pre>

</div>

<div id="compaction" class="section">
<h3><span class="secno">3.9 </span>Compaction</h3>

<p>Compaction is the process of taking a JSON-LD document and applying a 
context such that the most compact form of the document is generated. JSON
is typically expressed in a very compact, key-value format. That is, full
IRIs are rarely used as keys. At times, a JSON-LD document may be received
that is not in its most compact form. JSON-LD, via the API, provides a way
to compact a JSON-LD document.
</p>

<p>For example, assume the following JSON-LD input document:</p>

<pre class="example">
{
   "http://xmlns.com/foaf/0.1/name": "Manu Sporny",
   "http://xmlns.com/foaf/0.1/homepage": 
   {
      "@iri": "http://manu.sporny.org/"
   }
}</pre>

<p>Additionally, assume the following developer-supplied JSON-LD context:</p>

<pre class="example">
{
   "name": "http://xmlns.com/foaf/0.1/name",
   "homepage": "http://xmlns.com/foaf/0.1/homepage",
   "@coerce": 
   {
      "@iri": ["homepage"]
   }
}</pre>

<p>Running the JSON-LD Compaction algorithm given the context supplied above 
against the JSON-LD input document provided above would result in the following
output:</p>

<pre class="example">
{
   "name": "Manu Sporny",
   "homepage": "http://manu.sporny.org/",
   "@context": 
   {
      "name": "http://xmlns.com/foaf/0.1/name",
      "homepage": "http://xmlns.com/foaf/0.1/homepage",
      "@coerce": 
      {
         "@iri": "homepage"
      }
   }
}</pre>

<p>The compaction algorithm also enables the developer to map any expanded
format into an application-specific compacted format. While the context 
provided above mapped <code>http://xmlns.com/foaf/0.1/name</code> to
<strong>name</strong>, it could have also mapped it to any arbitrary string
provided by the developer.
</p>

</div>

<div id="expansion" class="section">
<h3><span class="secno">3.10 </span>Expansion</h3>

<p>Expansion is the process of taking a JSON-LD document and applying a 
context such that all IRI, datatypes, and literal values are expanded so
that the context is no longer necessary. JSON-LD document expansion 
is typically used when re-mapping JSON-LD documents to application-specific
JSON documents or as a part of the <a href="#normalization">Normalization</a>
process.</p>

<p>For example, assume the following JSON-LD input document:</p>

<pre class="example">
{
   "name": "Manu Sporny",
   "homepage": "http://manu.sporny.org/",
   "@context": 
   {
      "name": "http://xmlns.com/foaf/0.1/name",
      "homepage": "http://xmlns.com/foaf/0.1/homepage",
      "@coerce": 
      {
         "@iri": "homepage"
      }
   }
}</pre>

<p>Running the JSON-LD Expansion algorithm against the JSON-LD input document 
provided above would result in the following output:</p>

<pre class="example">
{
   "http://xmlns.com/foaf/0.1/name": "Manu Sporny",
   "http://xmlns.com/foaf/0.1/homepage": 
   {
      "@iri": "http://manu.sporny.org/"
   }
}</pre>

</div>

<div id="framing" class="section">
<h3><span class="secno">3.11 </span>Framing</h3>

<p>A JSON-LD document is a representation of a directed graph. A single
directed graph can have many different serializations, each expressing
exactly the same information. Developers typically work with trees, also
called associative arrays, when dealing with JSON. While mapping a graph to 
a tree can be done, the layout of the end result must be specified in advance. 
A <dfn title="Frame" id="dfn-frame">Frame</dfn> can be used by a developer on a JSON-LD document to 
specify a deterministic layout for a graph.
</p>

<p>Framing is the process of taking a JSON-LD document, which expresses a
graph of information, and applying a specific graph layout 
(called a <a class="tref internalDFN" title="Frame" href="#dfn-frame">Frame</a>).
</p>

<p>The JSON-LD document below expresses a library, a book and a chapter:</p>

<pre class="example">
{
   "@subject": 
   [{
      "@subject": "http://example.org/library",
      "@type": "ex:Library",
      "ex:contains": "http://example.org/library/the-republic"
   }, 
   {
      "@subject": "http://example.org/library/the-republic",
      "@type": "ex:Book",
      "dc:creator": "Plato",
      "dc:title": "The Republic",
      "ex:contains": "http://example.org/library/the-republic#introduction"
   }, 
   {
      "@subject": "http://example.org/library/the-republic#introduction",
      "@type": "ex:Chapter",
      "dc:description": "An introductory chapter on The Republic.",
      "dc:title": "The Introduction"
   }],
   "@context": 
   {
      "@coerce": 
      {
         "@iri": "ex:contains"
      },
      "dc": "http://purl.org/dc/elements/1.1/",
      "ex": "http://example.org/vocab#"
   }
}</pre>

<p>Developers typically like to operate on items in a hierarchical, tree-based
fashion. Ideally, a developer would want the data above sorted into top-level
libraries, then the books that are contained in each library, and then the
chapters contained in each book. To achieve that layout, the developer can
define the following <a class="tref internalDFN" title="frame" href="#dfn-frame">frame</a>:</p>

<pre class="example">
{
   "@context": {
      "dc": "http://purl.org/dc/elements/1.1/",
      "ex": "http://example.org/vocab#"
   },
   "@type": "ex:Library",
   "ex:contains": {
      "@type": "ex:Book",
      "ex:contains": {
         "@type": "ex:Chapter"
      }
   }
}</pre>

<p>When the framing algorithm is run against the previously defined 
JSON-LD document, paired with the <a class="tref internalDFN" title="frame" href="#dfn-frame">frame</a> above, the following
JSON-LD document is the end result:</p>

<pre class="example">
{
   "@context": 
   {
      "ex": "http://example.org/vocab#",
      "dc": "http://purl.org/dc/elements/1.1/"
   }
   "@subject": "http://example.org/library",
   "@type": "ex:Library",
   "ex:contains": 
   {
      "@subject": "http://example.org/library/the-republic",
      "@type": "ex:Book",
      "dc:creator": "Plato",
      "dc:title": "The Republic",
      "ex:contains": 
      {
         "@subject": "http://example.org/library/the-republic#introduction",
         "@type": "ex:Chapter",
         "dc:description": "An introductory chapter on The Republic.",
         "dc:title": "The Introduction"
      },
   },
}</pre>

<p>The JSON-LD framing algorithm allows developers to query by example and
force a specific tree layout to a JSON-LD document.
</p>

</div>

</div>

<div id="advanced-concepts" class="section">

<!-- OddPage -->
<h2><span class="secno">4. </span>Advanced Concepts</h2>

<p>JSON-LD has a number of features that provide functionality above and beyond
the core functionality described above. The following sections outline the
features that are specific to JSON-LD.
</p>

<div id="automatic-typing" class="section">
<h3><span class="secno">4.1 </span>Automatic Typing</h3>

<p>Since JSON is capable of expressing typed information such as doubles, 
integers, and boolean values. As demonstrated below, JSON-LD utilizes that 
information to create <a class="tref internalDFN" title="typed_literal" href="#dfn-typed_literal">typed literal</a>s:</p>

<pre class="example">
{
...
  // The following two values are automatically converted to a type of xsd:double
  // and both values are equivalent to each other.
  "measure:cups": <span class="diff">5.3</span>,
  "measure:cups": <span class="diff">5.3e0</span>,
  // The following value is automatically converted to a type of xsd:double as well
  "space:astronomicUnits": <span class="diff">6.5e73</span>,
  // The following value should never be converted to a language-native type
  "measure:stones": <span class="diff">{ "@literal": "4.8", "@datatype": "xsd:decimal" }</span>,
  // This value is automatically converted to having a type of xsd:integer
  "chem:protons": <span class="diff">12</span>,
  // This value is automatically converted to having a type of xsd:boolean
  "sensor:active": <span class="diff">true</span>,
...
}</pre>

<p class="note">When dealing with a number of modern programming languages,
including JavaScript ECMA-262, there is no distinction between 
<strong>xsd:decimal</strong> and <strong>xsd:double</strong> values. That is, 
the number <code>5.3</code> and the number 
<code>5.3e0</code> are treated as if they were the same. When converting from 
JSON-LD to a language-native format and back, datatype information is lost in a 
number of these languages. Thus, one could say that <code>5.3</code> is a 
<strong>xsd:decimal</strong> and <code>5.3e0</code> is an 
<strong>xsd:double</strong> in JSON-LD, but when both values are 
converted to a language-native format the datatype difference between the two 
is lost because the machine-level representation will almost always be a 
<strong>double</strong>. 
Implementers should be aware of this potential round-tripping issue between 
<strong>xsd:decimal</strong> and <strong>xsd:double</strong>. Specifically
objects with a datatype of <strong>xsd:decimal</strong> <em class="rfc2119" title="must not">must not</em> be converted
to a language native type.
</p>

</div>

<div id="type-coercion" class="section">
<h3><span class="secno">4.2 </span>Type Coercion</h3>

<p>JSON-LD supports the coercion of values to particular data types. 
Type coercion allows someone deploying JSON-LD to coerce the incoming or 
outgoing types to the proper data type based on a mapping of data type IRIs to 
property types. Using type coercion, one may convert simple JSON data to 
properly typed RDF data.</p>

<p>The example below demonstrates how a JSON-LD author can coerce values to 
<a class="tref internalDFN" title="plain_literal" href="#dfn-plain_literal">plain literal</a>s, <a class="tref internalDFN" title="typed_literal" href="#dfn-typed_literal">typed literal</a>s and IRIs.</p>

<pre class="example">
{
  "@context": 
  {  
     "rdf": "http://www.w3.org/1999/02/22-rdf-syntax-ns#",
     "xsd": "http://www.w3.org/2001/XMLSchema#",
     "name": "http://xmlns.com/foaf/0.1/name",
     "age": "http://xmlns.com/foaf/0.1/age",
     "homepage": "http://xmlns.com/foaf/0.1/homepage",
<span class="diff">     "@coerce":
     {
        "xsd:integer": "age",
        "@iri": "homepage",
     }</span>
  },
  "name": "John Smith",
  "age": <span class="diff">"41"</span>,
  "homepage": <span class="diff">"http://example.org/home/"</span>
}</pre>

<p>The example above would generate the following triples:</p>

<pre class="example">
_:bnode1
   &lt;http://xmlns.com/foaf/0.1/name&gt;
      "John Smith" .
_:bnode1
   &lt;http://xmlns.com/foaf/0.1/age&gt;
      "41"^^http://www.w3.org/2001/XMLSchema#integer .
_:bnode1
   &lt;http://xmlns.com/foaf/0.1/homepage&gt;
      &lt;http://example.org/home/&gt; .</pre>

</div>

<div id="chaining" class="section">
  <h3><span class="secno">4.3 </span>Chaining</h3>
  <p>
    Object <dfn title="chaining" id="dfn-chaining">chaining</dfn> is a JSON-LD feature that allows an author to 
    use the definition of JSON-LD objects as <a class="tref internalDFN" title="property" href="#dfn-property">property</a> values. This 
    is a commonly used mechanism for creating a parent-child relationship 
    between two <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a>s.
  </p>
  <p>The example shows an two subjects related by a property from the first 
  subject:</p>

  <pre class="example">
{
...
  "foaf:name": "Manu Sporny",
  "<span class="diff">foaf:knows</span>": {
    "<span class="diff">@type</span>": "<span class="diff">foaf:Person</span>",
    "<span class="diff">foaf:name</span>": "<span class="diff">Gregg Kellogg</span>",
  }
...
}</pre>
  
  <p>
    An object definition, like the one used above, <em class="rfc2119" title="may">may</em> be used as a 
    JSON value at any point in JSON-LD.
  </p>
</div>

<div id="identifying-unlabeled-nodes" class="section">
<h3><span class="secno">4.4 </span>Identifying Unlabeled Nodes</h3>

<p>At times, it becomes necessary to be able to express information without
being able to specify the subject. Typically, this type of node is called
an unlabeled node or a blank node. In JSON-LD, unlabeled node identifiers are 
automatically created if a subject is not specified using the 
<code>@subject</code> keyword. However, authors may provide identifiers for
unlabeled nodes by using the special <code>_</code> (underscore) CURIE 
prefix.</p>

<pre class="example">
{
...
  "@subject": "<span class="diff">_:foo</span>",
...
}</pre>

<p>The example above would set the subject to <code>_:foo</code>, which can
then be used later on in the JSON-LD markup to refer back to the 
unlabeled node. This practice, however, is usually frowned upon when
generating Linked Data. If a developer finds that they refer to the unlabeled
node more than once, they should consider naming the node using a resolve-able
IRI.
</p>

</div>

<div id="overriding-keywords" class="section">
<h3><span class="secno">4.5 </span>Overriding Keywords</h3>

<p>JSON-LD allows all of the syntax keywords, except for <code>@context</code>,
to be overridden. This feature allows more legacy JSON content to be supported 
by JSON-LD. It also allows developers to design domain-specific implementations 
using only the JSON-LD context.</p>

<pre class="example">
{
  "@context": 
  {  
     <span class="diff">"url": "@subject"</span>,
     <span class="diff">"a": "@type"</span>,
     "name": "http://schema.org/name"
  },
  "url": "http://example.com/about#gregg",
  "a": "http://schema.org/Person",
  "name": "Gregg Kellogg"
}</pre>

<p>In the example above, the <code>@subject</code> and <code>@type</code> 
keywords have been overridden by <strong>url</strong> and 
<strong>a</strong>, respectively.
</p>

</div>

<div id="normalization" class="section">
<h3><span class="secno">4.6 </span>Normalization</h3>

<p>Normalization is the process of taking a JSON-LD document and performing a 
deterministic transformation on that document that results in a final document
that any conforming JSON-LD processor would have generated given the same
input document. The problem is a fairly difficult technical problem to solve
because it requires a directed graph to be ordered into a set of nodes and
edges in a deterministic way. This is easy to do when all of the nodes have
unique names, but very difficult to do when some of the nodes are unlabeled.
</p>

<p>Normalization is useful when comparing two graphs against one another,
when generating a detailed list of differences between two graphs, and
when generating a cryptographic digital signature for information contained 
in a graph or when generating a hash of the information contained in a graph.
</p>

<p>The example below is an un-normalized JSON-LD document:</p>

<pre class="example">
{
   "name": "Manu Sporny",
   "homepage": "http://manu.sporny.org/",
   "@context": 
   {
      "name": "http://xmlns.com/foaf/0.1/name",
      "homepage": "http://xmlns.com/foaf/0.1/homepage",
      "xsd": "http://www.w3.org/2001/XMLSchema#",
      "@coerce": 
      {
         "@iri": ["homepage"]
      }
   }
}</pre>

<p>The example below is the normalized form of the JSON-LD document above:</p>

<p class="note">Whitespace is used below to aid readability. The normalization
algorithm for JSON-LD remove all unnecessary whitespace in the fully 
normalized form.</p>

<pre class="example">
[{
    "@subject": 
    {
        "@iri": "_:c14n0"
    },
    "http://xmlns.com/foaf/0.1/homepage": 
    {
        "@iri": "http://manu.sporny.org/"
    },
    "http://xmlns.com/foaf/0.1/name": "Manu Sporny"
}]</pre>

<p>Notice how all of the <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s have been expanded and sorted in
alphabetical order. Also, notice how the <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a> has been 
labeled with a blank node identifier. Normalization ensures that any arbitrary
graph containing exactly the same information would be normalized to exactly
the same form shown above.</p>

</div>

</div>

<div id="algorithms" class="section">

<!-- OddPage -->
<h2><span class="secno">5. </span>Algorithms</h2>

<div id="compaction-1" class="section">
<h3><span class="secno">5.1 </span>Compaction</h3>
<p class="issue">TBD: Explain compaction algorithm.</p>
</div>

<div id="expansion-1" class="section">
<h3><span class="secno">5.2 </span>Expansion</h3>
<p class="issue">TBD: Explain expansion algorithm.</p>
</div>

<div id="framing-1" class="section">
<h3><span class="secno">5.3 </span>Framing</h3>
<p class="issue">TBD: Explain framing algorithm.</p>
</div>

<div id="normalization-1" class="section">
<h3><span class="secno">5.4 </span>Normalization</h3>
<p class="issue">TBD: Explain normalization algorithm.</p>
</div>

<div id="rdf-conversion" class="section">
<h3><span class="secno">5.5 </span>RDF Conversion</h3>

<p>A JSON-LD document <em class="rfc2119" title="may">may</em> be converted to any other RDF-compatible document
format using the algorithm specified in this section.</p>

<p>
  The JSON-LD Processing Model describes processing rules for extracting RDF
  from a JSON-LD document. Note that many uses of JSON-LD may not require 
  generation of RDF.
</p>

<p>
The processing algorithm described in this section is provided in
order to demonstrate how one might implement a JSON-LD to RDF processor. 
Conformant implementations are only required to produce the same type and
number of triples during the output process and are not required to 
implement the algorithm exactly as described.
</p>

<p class="issue">The RDF Conversion Algorithm is a work in progress.</p>

<div class="informative section" id="overview">
  <h4><span class="secno">5.5.1 </span>Overview</h4><p><em>This section is non-normative.</em></p>
  <p>
    JSON-LD is intended to have an easy to parse grammar that closely models existing
    practice in using JSON for describing object representations. This allows the use
    of existing libraries for parsing JSON in a document-oriented fashion, or can allow
    for stream-based parsing similar to SAX.
  </p>
  <p>
    As with other grammars used for describing <a class="tref internalDFN" title="Linked_Data" href="#dfn-linked_data">Linked Data</a>, a key concept is that of
    a <em>resource</em>. Resources may be of three basic types: <em>IRI</em>s, for describing
    externally named entities, <em>BNodes</em>, resources for which an external name does not
    exist, or is not known, and Literals, which describe terminal entities such as strings,
    dates and other representations having a lexical representation possibly including
    an explicit language or datatype.
  </p>
  <p>
    Data described with JSON-LD may be considered to be the representation of a graph made
    up of <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a> and <a class="tref internalDFN" title="object" href="#dfn-object">object</a> resources related via a <a class="tref internalDFN" title="property" href="#dfn-property">property</a> resource.
    However, specific implementations may choose to operate on the document as a normal
    JSON description of objects having attributes.
  </p>
</div>

<div id="processing-algorithm-terms" class="section">
  <h4><span class="secno">5.5.2 </span>Processing Algorithm Terms</h4>
  <dl>
    <dt><dfn title="initial_context" id="dfn-initial_context">initial context</dfn></dt>
    <dd>
      a context that is specified to the JSON-LD processing algorithm
      before processing begins.
    </dd>
    <dt><dfn title="default_graph" id="dfn-default_graph">default graph</dfn></dt>
    <dd>
      the destination graph for all triples generated by JSON-LD markup.
    </dd>
    <dt><dfn title="active_subject" id="dfn-active_subject">active subject</dfn></dt>
    <dd>
      the currently active subject that the processor should use when
      generating triples.
    </dd>
    <dt><dfn title="active_property" id="dfn-active_property">active property</dfn></dt>
    <dd>
      the currently active property that the processor should use when
      generating triples.
    </dd>
    <dt><dfn title="active_object" id="dfn-active_object">active object</dfn></dt>
    <dd>
      the currently active object that the processor should use when
      generating triples.
    </dd>
    <dt><dfn title="active_context" id="dfn-active_context">active context</dfn></dt>
    <dd>
      a context that is used to resolve CURIEs while the processing
      algorithm is running. The <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a> is the context contained within the
      <a class="tref internalDFN" title="processor_state" href="#dfn-processor_state">processor state</a>.
    </dd>
    <dt><dfn title="local_context" id="dfn-local_context">local context</dfn></dt>
    <dd>
      a context that is specified at the JSON associative-array level,
      specified via the <code>@context</code> keyword.
    </dd>
    <dt><dfn title="processor_state" id="dfn-processor_state">processor state</dfn></dt>
    <dd>
      the <a class="tref internalDFN" title="processor_state" href="#dfn-processor_state">processor state</a>, which includes the <a class="tref" title="active__context">active
      context</a>, <a class="tref" title="current_subject">current subject</a>, and <a class="tref" title="current_property">current property</a>. The <a class="tref" title="processor__state">processor
      state</a> is managed as a stack with elements from the previous <a class="tref internalDFN" title="processor_state" href="#dfn-processor_state">processor state</a>
      copied into a new <a class="tref internalDFN" title="processor_state" href="#dfn-processor_state">processor state</a> when entering a new associative array.
    </dd>
  </dl>
</div>

<div id="processing-tokens-and-keywords" class="section">
  <h4><span class="secno">5.5.3 </span>Processing Tokens and Keywords</h4>
  <dl>
  <dt><code>@context</code></dt><dd>Used to set the <a class="tref internalDFN" title="local_context" href="#dfn-local_context">local context</a>.</dd>
  <dt><code>@base</code></dt><dd>Used to set the base IRI for all object IRIs affected  by the <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a>.</dd>
  <dt><code>@vocab</code></dt><dd>Used to set the base IRI for all property IRIs affected by the <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a>.</dd>
  <dt><code>@coerce</code></dt><dd>Used to specify type coercion rules.</dd>
  <dt><code>@literal</code></dt><dd>Used to specify a literal value.</dd>
  <dt><code>@iri</code></dt><dd>Used to specify an IRI value.</dd>
  <dt><code>@language</code></dt><dd>Used to specify the language for a literal.</dd>
  <dt><code>@datatype</code></dt><dd>Used to specify the datatype for a literal.</dd>
  <dt><code>:</code></dt><dd>The separator for CURIEs when used in JSON keys or JSON values.</dd>
  <dt><code>@subject</code></dt><dd>Sets the active subjects.</dd>
  <dt><code>@type</code></dt><dd>Used to set the rdf:type of the active subjects. This token may be conferred as syntactic sugar for rdf:type.</dd>
  </dl>
</div>

<div id="context-1" class="section">
  <h4 id="context"><span class="secno">5.5.4 </span>Context</h4>
  <p>
    Processing of JSON-LD is managed recursively using a process described in <a href="sequence">Sequence</a>.
    During processing, each rule is applied using information provided by the <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a>.
    Processing begins by pushing a new <a class="tref internalDFN" title="processor_state" href="#dfn-processor_state">processor state</a> onto the <a class="tref internalDFN" title="processor_state" href="#dfn-processor_state">processor state</a> stack and
    initializing the <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a> with the <a class="tref internalDFN" title="initial_context" href="#dfn-initial_context">initial context</a>. If a <a class="tref internalDFN" title="local_context" href="#dfn-local_context">local context</a> is encountered,
    information from the <a class="tref internalDFN" title="local_context" href="#dfn-local_context">local context</a> is merged into the <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a>.
  </p>
  <p class="issue">Should the document URL be used as the default for <code>@base</code> in the <a class="tref internalDFN" title="initial_context" href="#dfn-initial_context">initial context</a>?</p>
  <p>
    The <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a> is used for expanding keys and values of an associative array (or elements
    of a list (see <span a="#list-processing">List Processing</span>)).
  </p>
  <p>
    A <a class="tref internalDFN" title="local_context" href="#dfn-local_context">local context</a> is identified within an associative array having a key of <code>@context</code> with an associative
    array value. When processing a <a class="tref internalDFN" title="local_context" href="#dfn-local_context">local context</a>, special rules apply:
  </p>
  <ul>
    <li>The key <code>@base</code> <em class="rfc2119" title="must">must</em> have a value of a simple string with the lexical
    form of IRI and is saved in the <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a> to perform term mapping as described in <a href="#iri-processing">IRI Processing</a>.</li>
    <li>The key <code>@vocab</code> <em class="rfc2119" title="must">must</em> have a value of a simple string with the lexical
    form of IRI and is saved in the <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a> to perform term mapping as described in <a href="#iri-processing">IRI Processing</a>.</li>
    <li>The key <code>@coerce</code> <em class="rfc2119" title="must">must</em> have a value of an associative array. Processing
      of the associative array is described <a href="#coerce">below</a></li>
    <li>Otherwise, the key <em class="rfc2119" title="must">must</em> have the lexical form of
      <cite><a href="http://www.w3.org/TR/2009/REC-xml-names-20091208/#NT-NCName">NCName</a></cite>
      and <em class="rfc2119" title="must">must</em> have the value of a simple string with the lexical form of IRI.
      Merge each key-value pair into the <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a>, overwriting
      any duplicate values.
    </li>
  </ul>
  <div class="section">
    <h5 id="coerce">Coerce</h5>
    <p>
      Map each key-value pair in the <a class="tref internalDFN" title="local_context" href="#dfn-local_context">local context</a>'s
      <code>@coerce</code> mapping into the <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a>'s
      <code>@coerce</code> mapping, overwriting any duplicate values in 
      the <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a>'s <code>@coerce</code> mapping.
      The <code>@coerce</code> mapping has either a single CURIE or an
      array of CURIEs. When merging with an existing mapping in the <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a>,
      map all CURIE values to array form and replace with the union of the value from
      the <a class="tref internalDFN" title="local_context" href="#dfn-local_context">local context</a> and the value of the <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a>. If the result is an array
      with a single CURIE, the processor <em class="rfc2119" title="may">may</em> represent this as a string value.
    </p>
  </div>
</div>

<div id="iri-processing" class="section">
  <h4><span class="secno">5.5.5 </span>IRI Processing</h4>
  <p>Keys and some values are evaluated to produce an IRI. This section defines an algorithm for
    transforming a value representing an IRI into an actual IRI.</p>
  <p>IRIs may be represented as an explicit string, or as a CURIE, as a value relative to <code>@base</code>
    or <code>@vocab</code>.</p>
  <p>
    CURIEs are defined more formally in [<cite><a class="bibref" rel="biblioentry" href="#bib-RDFA-CORE">RDFA-CORE</a></cite>] <cite><a href="http://www.w3.org/TR/rdfa-core/#s_curies">section 6 "CURIE Syntax Definition"</a></cite>.
    Generally, a CURIE is composed of a <em>prefix</em> and a <em>suffix</em> separated by a ':'. In
    JSON-LD, either the prefix may be the empty string, denoting the <dfn title="default_prefix" id="dfn-default_prefix">default prefix</dfn>.
  </p>
  <p>The procedure for generating an IRI is:
    </p><ol class="algorithm">
      <li>Split the value into a <em>prefix</em> and <em>suffix</em> from the first occurrence of ':'.</li>
      <li>If the prefix is a '_', generate a named BNode using the suffix as the name.</li>
      <li>If the <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a> contains a mapping for <em>prefix</em>, generate an IRI
        by prepending the mapped prefix to the (possibly empty) suffix. Note that an empty
        suffix and no suffix (meaning the value contains no ':' string at all) are treated equivalently.</li>
      <li>If the IRI being processed is for a property (i.e., a key value in an associative array, or a
        value in a <code>@coerce</code> mapping) and the active context has a <code>@vocab</code> mapping,
        join the mapped value to the suffix using the method described in [<cite><a class="bibref" rel="biblioentry" href="#bib-RFC3987">RFC3987</a></cite>].</li>
      <li>If the IRI being processed is for a subject or object (i.e., not a property) and the active context has a <code>@base</code> mapping,
        join the mapped value to the suffix using the method described in [<cite><a class="bibref" rel="biblioentry" href="#bib-RFC3987">RFC3987</a></cite>].</li>
      <li>Otherwise, use the value directly as an IRI.</li>
    </ol>
  <p></p>
</div>

<div id="sequence" class="section">
  <h4><span class="secno">5.5.6 </span>Sequence</h4>

  <p>
    The algorithm below is designed for in-memory implementations with random access to associative
    array elements.
  </p>
  <p>
    A conforming JSON-LD processor <em class="rfc2119" title="must">must</em> implement a
    processing algorithm that results in the same <a class="tref internalDFN" title="default_graph" href="#dfn-default_graph">default graph</a> that the following
    algorithm generates:
  </p>

  <ol class="algorithm">
    <li id="processing-step-default-context">
      Create a new <a class="tref internalDFN" title="processor_state" href="#dfn-processor_state">processor state</a> with with the <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a> set to the
      <a class="tref internalDFN" title="initial_context" href="#dfn-initial_context">initial context</a> and <a class="tref internalDFN" title="active_subject" href="#dfn-active_subject">active subject</a> and <a class="tref internalDFN" title="active_property" href="#dfn-active_property">active property</a>
      initialized to NULL.
    </li>

    <li id="processing-step-associative">
      If an associative array is detected, perform the following steps:
      <ol class="algorithm">
        <li>
          If the associative array has a <code>@context</code> key, process the local context as
          described in <a href="#context">Context</a>.
        </li>
        <li>
          If the associative array has an <code>@iri</code> key, set the <a class="tref internalDFN" title="active_object" href="#dfn-active_object">active object</a> by
          performing <a href="#iri-processing">IRI Processing</a> on the associated value. Generate a
          triple representing the <a class="tref internalDFN" title="active_subject" href="#dfn-active_subject">active subject</a>, the <a class="tref internalDFN" title="active_property" href="#dfn-active_property">active property</a> and the
          <a class="tref internalDFN" title="active_object" href="#dfn-active_object">active object</a>. Return the <a class="tref internalDFN" title="active_object" href="#dfn-active_object">active object</a> to the calling location.
        </li>
        <li>
          If the associative array has a <code>@literal</code> key, set the <a class="tref internalDFN" title="active_object" href="#dfn-active_object">active object</a>
          to a literal value as follows:
          <ul>
            <li>
              as a <a class="tref internalDFN" title="typed_literal" href="#dfn-typed_literal">typed literal</a> if the associative array contains a <code>@datatype</code> key
              after performing <a href="#iri-processing">IRI Processing</a> on the specified<code>@datatype</code>.
            </li>
            <li>
              otherwise, as a <a class="tref internalDFN" title="plain_literal" href="#dfn-plain_literal">plain literal</a>. If the associative array contains
              a <code>@language</code> key, use it's value to set the language of the plain literal.
            </li>
          </ul>
          Generate a triple representing the <a class="tref internalDFN" title="active_subject" href="#dfn-active_subject">active subject</a>, the <a class="tref" title="active__property">active
          property</a> and the <a class="tref internalDFN" title="active_object" href="#dfn-active_object">active object</a>. Return the <a class="tref internalDFN" title="active_object" href="#dfn-active_object">active object</a> to the calling location.
        </li>
        <li>If the associative array has a <code>@</code> key:
          <ol class="algorithm">
            <li>
              If the value is a string, set the <a class="tref internalDFN" title="active_object" href="#dfn-active_object">active object</a> to the result of performing
              <a href="#iri-processing">IRI Processing</a>. Generate a
              triple representing the <a class="tref internalDFN" title="active_subject" href="#dfn-active_subject">active subject</a>, the <a class="tref internalDFN" title="active_property" href="#dfn-active_property">active property</a> and the
              <a class="tref internalDFN" title="active_object" href="#dfn-active_object">active object</a>. Set the <a class="tref internalDFN" title="active_subject" href="#dfn-active_subject">active subject</a> to the <a class="tref internalDFN" title="active_object" href="#dfn-active_object">active object</a>.
            </li>
            <li>
              Create a new <a class="tref internalDFN" title="processor_state" href="#dfn-processor_state">processor state</a> using copies of the <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a>,
              <a class="tref internalDFN" title="active_subject" href="#dfn-active_subject">active subject</a> and <a class="tref internalDFN" title="active_property" href="#dfn-active_property">active property</a> and process the value
              starting at <a href="#processing-step-associative">Step 2</a>, set the <a class="tref" title="active__subject">active
              subject</a> to the result and proceed using the previous <a class="tref internalDFN" title="processor_state" href="#dfn-processor_state">processor state</a>.
            </li>
          </ol>
        </li>
        <li>
          If the associative array does not have a <code>@</code> key, set the <a class="tref" title="active__object">active
          object</a> to newly generated <a class="tref" title="blank_node_identifier">blank node identifier</a>. Generate a triple
          representing the <a class="tref internalDFN" title="active_subject" href="#dfn-active_subject">active subject</a>, the <a class="tref internalDFN" title="active_property" href="#dfn-active_property">active property</a> and the
          <a class="tref internalDFN" title="active_object" href="#dfn-active_object">active object</a>. Set the <a class="tref internalDFN" title="active_subject" href="#dfn-active_subject">active subject</a> to the <a class="tref" title="active__object">active
          object</a>.
        </li>
        <li>
          For each key in the associative array that has not already been processed, perform
          the following steps:
          <ol class="algorithm">
            <li>If the key is <code>a</code>, set the <a class="tref internalDFN" title="active_property" href="#dfn-active_property">active property</a> 
            to <code>rdf:type</code>.
            </li>
            <li>Otherwise, set the <a class="tref internalDFN" title="active_property" href="#dfn-active_property">active property</a> to the result of performing
            <a href="#iri-processing">IRI Processing</a> on the key.</li>
            <li>
              Create a new <a class="tref internalDFN" title="processor_state" href="#dfn-processor_state">processor state</a> copies of the <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a>,
              <a class="tref internalDFN" title="active_subject" href="#dfn-active_subject">active subject</a> and <a class="tref internalDFN" title="active_property" href="#dfn-active_property">active property</a> and process the value
              starting at <a href="#processing-step-associative">Step 2</a> and proceed using the
              previous <a class="tref internalDFN" title="processor_state" href="#dfn-processor_state">processor state</a>.
            </li>
          </ol>
        </li>
        <li>
          Return the <a class="tref internalDFN" title="active_object" href="#dfn-active_object">active object</a> to the calling location.
        </li>
      </ol>
    </li>

    <li>
      If a regular array is detected, process each value in the array by doing the following
      returning the result of processing the last value in the array:

      <ol class="algorithm">
        <li>
          If the value is a regular array, generate an RDF List by linking
          each element of the list using <code>rdf:first</code> and <code>rdf:next</code>, terminating the list with <code>rdf:nil</code>
          using the following sequence:
          <ol>
            <li>
              If the list has no element, generate a triple using the <a class="tref internalDFN" title="active_subject" href="#dfn-active_subject">active subject</a>, <a class="tref internalDFN" title="active_property" href="#dfn-active_property">active property</a>
              and <code>rdf:nil</code>.
            </li>
            <li>
              Otherwise, generate a triple using using the <a class="tref internalDFN" title="active_subject" href="#dfn-active_subject">active subject</a>, <a class="tref internalDFN" title="active_property" href="#dfn-active_property">active property</a>
              and a newly generated BNode identified as <em>first bnode</em>.
            </li>
            <li>
              For each element other than the last element in the list:
              <ol>
                <li>Create a processor state using the active context, <em>first bnode</em> as the <a class="tref internalDFN" title="active_subject" href="#dfn-active_subject">active subject</a>, and <code>rdf:first</code> as the <a class="tref internalDFN" title="active_property" href="#dfn-active_property">active property</a>.</li>
                <li>Unless this is the last element in the list, generate a new BNode identified as <em>rest bnode</em>, otherwise use <code>rdf:nil</code>.</li>
                <li>Generate a new triple using <em>first bnode</em>, <code>rdf:rest</code> and <em>rest bnode</em>.</li>
                <li>Set <em>first bnode</em> to <em>rest bnode</em>.</li>
              </ol>
            </li>
          </ol>
        </li>
        <li>
          Otherwise, create a new <a class="tref internalDFN" title="processor_state" href="#dfn-processor_state">processor state</a> copies of the <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a>,
          <a class="tref internalDFN" title="active_subject" href="#dfn-active_subject">active subject</a> and <a class="tref internalDFN" title="active_property" href="#dfn-active_property">active property</a> and process the value
          starting at <a href="#processing-step-associative">Step 2</a> and proceed using the
          previous <a class="tref internalDFN" title="processor_state" href="#dfn-processor_state">processor state</a>.
        </li>
      </ol>
    </li>
    
    <li>
      If a string is detected, generate a triple using the <a class="tref internalDFN" title="active_subject" href="#dfn-active_subject">active subject</a>, <a class="tref internalDFN" title="active_object" href="#dfn-active_object">active object</a>
      and a <a class="tref internalDFN" title="plain_literal" href="#dfn-plain_literal">plain literal</a> value created from the string.
    </li>
    
    <li>
      If a number is detected, generate a <a class="tref internalDFN" title="typed_literal" href="#dfn-typed_literal">typed literal</a> using a string representation of
      the value with datatype set to either <code>xsd:integer</code> or
      <code>xsd:double</code>, depending on if the value contains a
      fractional and/or an exponential component. Generate a triple using the <a class="tref" title="active__subject">active
      subject</a>, <a class="tref internalDFN" title="active_object" href="#dfn-active_object">active object</a> and the generated typed literal.
    </li>
    
    <li>
      Otherwise, if <strong>true</strong> or <strong>false</strong> is detected,
      generate a triple using the <a class="tref internalDFN" title="active_subject" href="#dfn-active_subject">active subject</a>, <a class="tref internalDFN" title="active_object" href="#dfn-active_object">active object</a>
      and a <a class="tref internalDFN" title="typed_literal" href="#dfn-typed_literal">typed literal</a> value created from the string representation of the
      value with datatype set to <code>xsd:boolean</code>.
    </li>
  </ol>
</div>


<!--  THIS SHOULD BE SPLIT OUT INTO A SEPARATE DOCUMENT 

<section>
<h1>Best Practices</h1>

<p>The nature of Web programming allows one to use basic technologies, such as
JSON-LD, across a variety of systems and environments. This section attempts to
describe some of those environments and the way in which JSON-LD can be 
integrated in order to help alleviate certain development headaches.
</p>

<section>
<h2>JavaScript</h2>

<p class="issue">It is expected that JSON-LD will be used quite a bit in 
JavaScript environments, however, features like the expanded form for
object values mean that using JSON-LD directly in JavaScript may be 
annoying without a middleware layer such as a simple library that 
converts JSON-LD markup before JavaScript uses it. One could say that JSON-LD
is a good fit for the RDF API, which enables a variety of RDF-based
Web Applications, but some don't want to require that level of functionality 
just to use JSON-LD. The group is still discussing the best way to proceed, 
so input on how JSON-LD could more easily be utilized in JavaScript 
environments would be very much appreciated.
</p>
</section>

<section>
<h2>Schema-less Databases</h2>

<p class="issue">Databases such as CouchDB and MongoDB allow the creation of
schema-less data stores. RDF is a type of schema-less data model and thus
lends itself to databases such as CouchDB and MongoDB. Both of these databases
can use JSON-LD as their storage format. The group needs feedback from 
CouchDB and MongoDB experts regarding the usefulness of JSON-LD in those
environments.</p>

<p class="issue">MongoDB does not allow the '.' character to be used in
key names. This prevents developers from storing IRIs as keys, which also
prevents storage of the data in normalized form. While this issue can
be avoided by using CURIEs for key values, it is not known if this
mechanism is enough to allow JSON-LD to be used in MongoDB in a way that
is useful to developers.
</p>

 -->

</div>

</div>

<div id="experimental-concepts" class="section">

<!-- OddPage -->
<h2><span class="secno">6. </span>Experimental Concepts</h2>

<p class="issue">There are a few advanced concepts where it is not clear 
whether or not the JSON-LD specification is going to support the complexity 
necessary to support each concept. The entire section on Advanced Concepts 
should be considered as discussion points; it is merely a list of 
possibilities where all of the benefits and drawbacks have not been explored.
</p>

<div id="disjoint-graphs" class="section">
<h3><span class="secno">6.1 </span>Disjoint Graphs</h3>

<p>When serializing an RDF graph that contains two or more sections of the
graph which are entirely disjoint, one must use an array to express the graph
as two graphs. This may not be acceptable to some authors, who would rather
express the information as one graph. Since, by definition, disjoint graphs
require there to be two top-level objects, JSON-LD utilizes a mechanism that
allows disjoint graphs to be expressed using a single graph.</p>

<p>Assume the following RDF graph:</p>

<pre class="example">
&lt;http://example.org/people#john&gt; 
   &lt;http://www.w3.org/1999/02/22-rdf-syntax-ns#type&gt;
      &lt;http://xmlns.com/foaf/0.1/Person&gt; .
&lt;http://example.org/people#jane&gt; 
   &lt;http://www.w3.org/1999/02/22-rdf-syntax-ns#type&gt;
      &lt;http://xmlns.com/foaf/0.1/Person&gt; .</pre>

<p>Since the two subjects are entirely disjoint with one another, it is
impossible to express the RDF graph above using a single JSON-LD associative
array.</p>

<p>In JSON-LD, one can use the subject to express disjoint graphs as a 
single graph:</p>

<pre class="example">
{
  "@": 
  [
    {
      "@": "http://example.org/people#john",
      "a": "foaf:Person"
    },
    {
      "@": "http://example.org/people#jane",
      "a": "foaf:Person"
    }
  ]
}</pre>

<p>A disjoint graph could also be expressed like so:</p>

<pre class="example">
[
  {
    "@": "http://example.org/people#john",
    "a": "foaf:Person"
  },
  {
    "@": "http://example.org/people#jane",
    "a": "foaf:Person"
  }
]</pre>

</div>

<div id="the-json-ld-api" class="section">
<h3><span class="secno">6.2 </span>The JSON-LD API</h3>

<p>This API provides a clean mechanism that enables developers to convert 
JSON-LD data into a format that is easier to work with in various programming
languages.
</p>

<pre class="idl">
<span class="idlInterface" id="idl-def-JSONLDProcessor">[<span class="extAttr">NoInterfaceObject</span>]
interface <span class="idlInterfaceID">JSONLDProcessor</span> {
<span class="idlMethod">    <span class="idlMethType"><a>object</a></span> <span class="idlMethName"><a href="#widl-JSONLDProcessor-toProjection-object-DOMString-jsonld-object-template-DOMString-subject-JSONLDParserCallback-callback">toProjection</a></span> (<span class="idlParam">in <span class="idlParamType"><a>DOMString</a></span> <span class="idlParamName">jsonld</span></span>, <span class="idlParam">in <span class="idlParamType"><a>object</a>?</span> <span class="idlParamName">template</span></span>, <span class="idlParam">in <span class="idlParamType"><a>DOMString</a>?</span> <span class="idlParamName">subject</span></span>, <span class="idlParam">in optional <span class="idlParamType"><a>JSONLDParserCallback</a>?</span> <span class="idlParamName">callback</span></span>);</span>
<span class="idlMethod">    <span class="idlMethType"><a>Graph</a></span>  <span class="idlMethName"><a href="#widl-JSONLDProcessor-toGraph-Graph-DOMString-jsonld-JSONLDParserCallback-callback">toGraph</a></span> (<span class="idlParam">in <span class="idlParamType"><a>DOMString</a></span> <span class="idlParamName">jsonld</span></span>, <span class="idlParam">in optional <span class="idlParamType"><a>JSONLDParserCallback</a>?</span> <span class="idlParamName">callback</span></span>);</span>
};</span>
</pre><div id="methods" class="section"><h4><span class="secno">6.2.1 </span>Methods</h4><dl class="methods"><dt id="widl-JSONLDProcessor-toGraph-Graph-DOMString-jsonld-JSONLDParserCallback-callback"><code>toGraph</code></dt><dd>Parses JSON-LD and transforms the data into an Graph, which is 
  compatible with the RDF Interfaces API specification [<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-INTERFACES">RDF-INTERFACES</a></cite>]. 
  This method will 
  return <code>null</code> if there are any errors, or if the RDF Interfaces 
  API is not available for use.
  
  <table class="parameters"><tr><th>Parameter</th><th>Type</th><th>Nullable</th><th>Optional</th><th>Description</th></tr><tr><td class="prmName">jsonld</td><td class="prmType"><code><a>DOMString</a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc">The JSON-LD string to parse into the RDFGraph.</td></tr><tr><td class="prmName">callback</td><td class="prmType"><code><a>JSONLDParserCallback</a></code></td><td class="prmNullTrue">✔</td><td class="prmOptTrue">✔</td><td class="prmDesc">A callback that is called whenever a processing error occurs on
     the given JSON-LD string.</td></tr></table><div><em>No exceptions.</em></div><div><em>Return type: </em><code><a>Graph</a></code></div></dd><dt id="widl-JSONLDProcessor-toProjection-object-DOMString-jsonld-object-template-DOMString-subject-JSONLDParserCallback-callback"><code>toProjection</code></dt><dd>Parses JSON-LD text into an RDF API Projection object as specified
    by the RDF API specification [<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-API">RDF-API</a></cite>].
    If there are any errors, <code>null</code> is returned.
  
  <table class="parameters"><tr><th>Parameter</th><th>Type</th><th>Nullable</th><th>Optional</th><th>Description</th></tr><tr><td class="prmName">jsonld</td><td class="prmType"><code><a>DOMString</a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc">The JSON-LD string to parse into the Projection.</td></tr><tr><td class="prmName">template</td><td class="prmType"><code><a>object</a></code></td><td class="prmNullTrue">✔</td><td class="prmOptFalse">✘</td><td class="prmDesc">The Projection template to use when building the Projection.</td></tr><tr><td class="prmName">subject</td><td class="prmType"><code><a>DOMString</a></code></td><td class="prmNullTrue">✔</td><td class="prmOptFalse">✘</td><td class="prmDesc">The subject to use when building the Projection.</td></tr><tr><td class="prmName">callback</td><td class="prmType"><code><a>JSONLDParserCallback</a></code></td><td class="prmNullTrue">✔</td><td class="prmOptTrue">✔</td><td class="prmDesc">A callback that is called whenever a processing error occurs on
     the given JSON-LD string.</td></tr></table><div><em>No exceptions.</em></div><div><em>Return type: </em><code><a>object</a></code></div></dd></dl></div>

<p>The JSONLDParserCallback is called whenever a processing error occurs on
input data.</p>

<pre class="idl">
<span class="idlInterface" id="idl-def-JSONLDProcessorCallback">[<span class="extAttr">NoInterfaceObject Callback</span>]
interface <span class="idlInterfaceID">JSONLDProcessorCallback</span> {
<span class="idlMethod">    <span class="idlMethType"><a>void</a></span> <span class="idlMethName"><a href="#widl-JSONLDProcessorCallback-error-void-DOMString-error">error</a></span> (<span class="idlParam">in <span class="idlParamType"><a>DOMString</a></span> <span class="idlParamName">error</span></span>);</span>
};</span>
</pre><div id="methods-1" class="section"><h4><span class="secno">6.2.2 </span>Methods</h4><dl class="methods"><dt id="widl-JSONLDProcessorCallback-error-void-DOMString-error"><code>error</code></dt><dd>This callback is invoked whenever an error occurs during processing.
  
  <table class="parameters"><tr><th>Parameter</th><th>Type</th><th>Nullable</th><th>Optional</th><th>Description</th></tr><tr><td class="prmName">error</td><td class="prmType"><code><a>DOMString</a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc">A descriptive error string returned by the processor.</td></tr></table><div><em>No exceptions.</em></div><div><em>Return type: </em><code><a>void</a></code></div></dd></dl></div>

<p>The following example demonstrates how to convert JSON-LD to a projection
that is directly usable in a programming environment:
</p>

<pre class="example">
// retrieve JSON-LD from a Web Service
var jsonldString = fetchPerson();

// This map, usually defined once per script, defines how to map incoming 
// JSON-LD to JavaScript objects
var myTemplate = { "http://xmlns.com/foaf/0.1/name" : "name",
                   "http://xmlns.com/foaf/0.1/age" : "age",
                  "http://xmlns.com/foaf/0.1/homepage" : "homepage" };

// Map the JSON-LD to a language-native object
var person = jsonld.toProjection(jsonldString, myTemplate);

// Use the language-native object
alert(person.name + " is " + person.age + " years old. " +
      "Their homepage is: " + person.homepage);</pre>

<p>A JSON-LD Serializer is also available to map a language-native object
to JSON-LD.

</p><pre class="idl">
<span class="idlInterface" id="idl-def-JSONLDSerializer">[<span class="extAttr">NoInterfaceObject</span>]
interface <span class="idlInterfaceID">JSONLDSerializer</span> {
<span class="idlMethod">    <span class="idlMethType"><a>DOMString</a></span> <span class="idlMethName"><a href="#widl-JSONLDSerializer-normalize-DOMString-object-obj">normalize</a></span> (<span class="idlParam">in <span class="idlParamType"><a>object</a></span> <span class="idlParamName">obj</span></span>);</span>
};</span>
</pre><div id="methods-2" class="section"><h4><span class="secno">6.2.3 </span>Methods</h4><dl class="methods"><dt id="widl-JSONLDSerializer-normalize-DOMString-object-obj"><code>normalize</code></dt><dd>Serializes a language-native object into a normalized JSON-LD string.
  Normalization is important when performing things like equality comparison
  and digital signature creation and verification.
  
  <table class="parameters"><tr><th>Parameter</th><th>Type</th><th>Nullable</th><th>Optional</th><th>Description</th></tr><tr><td class="prmName">obj</td><td class="prmType"><code><a>object</a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc">An associative array of key-value pairs that should be converted
     to a JSON-LD string. It is assumed that a map already exists for the
     data.</td></tr></table><div><em>No exceptions.</em></div><div><em>Return type: </em><code><a>DOMString</a></code></div></dd></dl></div>

<h3 id="the-normalization-algorithm">The Normalization Algorithm</h3>

<p class="issue">This algorithm is very rough, untested, and probably contains
many bugs. Use at your own risk. It will change in the coming months.</p>

<p>The JSON-LD normalization algorithm is as follows:</p>

<ol class="algorithm">
  <li>Remove the <code>@context</code> key and preserve it as the 
  <dfn title="transformation_map" id="dfn-transformation_map">transformation map</dfn> while running this algorithm.</li>
  <li>For each key
   <ol class="algorithm">
    <li>If the key is a CURIE, expand the CURIE to an IRI using the
        <a class="tref internalDFN" title="transformation_map" href="#dfn-transformation_map">transformation map</a>.</li>
   </ol>
  </li>
  <li>For each value
   <ol class="algorithm">
    <li>If the value should be type coerced per the 
        <a class="tref internalDFN" title="transformation_map" href="#dfn-transformation_map">transformation map</a>, ensure that it is transformed to the
        new value.</li>
    <li>If the value is a CURIE, expand the CURIE to an IRI using the
        <a class="tref internalDFN" title="transformation_map" href="#dfn-transformation_map">transformation map</a>.</li>
    <li>If the value is a <a class="tref internalDFN" title="typed_literal" href="#dfn-typed_literal">typed literal</a> and the type is a CURIE,
        expand it to an IRI using the <a class="tref internalDFN" title="transformation_map" href="#dfn-transformation_map">transformation map</a>.</li>
    <li>When generating the final value, use expanded object value form to
      store all IRIs, typed literals and <a class="tref internalDFN" title="plain_literal" href="#dfn-plain_literal">plain literal</a>s with language
      information.</li>
   </ol>
  </li>
  <li>Output each sorted key-value pair without any extraneous whitespace. If 
  the value is an associative array, perform this algorithm, starting
  at step #1, recursively on the sub-tree. There should be no nesting in
  the outputted JSON data. That is, the top-most element should be an
  array. Each item in the array contains a single subject with a 
  corresponding array of properties in UTF-8 sort order. Any related 
  objects that are complex objects themselves should be given a top-level 
  object in the top-level array.</li>
  
</ol>

<p class="issue">Note that normalizing named blank nodes is impossible at
present since one would have to specify a blank node naming algorithm. For
the time being, you cannot normalize graphs that contain named blank
nodes. However, normalizing graphs that contain non-named blank nodes 
is supported.</p>

<pre class="example">
var myObj = { "@context" : { 
                "xsd" : "http://www.w3.org/2001/XMLSchema#",
                "name" : "http://xmlns.com/foaf/0.1/name",
                "age" : "http://xmlns.com/foaf/0.1/age",
                "homepage" : "http://xmlns.com/foaf/0.1/homepage",
                "@coerce": {
                   "xsd:nonNegativeInteger": "age",
                   "xsd:anyURI": "homepage"
                }
              },
              "name" : "Joe Jackson",
              "age" : "42",
              "homepage" : "http://example.org/people/joe" };

// Map the language-native object to JSON-LD
var jsonldText = jsonld.normalize(myObj);</pre>

<p>After the code in the example above has executed, the 
<strong>jsonldText</strong> value will be (line-breaks added for 
readability):</p>

<pre class="example">
[{"http://xmlns.com/foaf/0.1/age":{"@datatype":"http://www.w3.org/2001/XMLSchema#nonNegativeInteger","@literal":"42"},
"http://xmlns.com/foaf/0.1/homepage":{"@iri":"http://example.org/people/joe"},
"http://xmlns.com/foaf/0.1/name":"Joe Jackson"}]</pre>

<p>When normalizing <strong>xsd:double</strong> values, implementers <em class="rfc2119" title="must">must</em>
ensure that the normalized value is a string. In order to generate the
string from a <strong>double</strong> value, output equivalent to the
<code>printf("%1.6e", value)</code> function in C <em class="rfc2119" title="must">must</em> be used where
<strong>"%1.6e"</strong> is the string formatter and <strong>value</strong>
is the value to be converted.</p>

<p>To convert the a double value in JavaScript, implementers can use the 
following snippet of code:</p>

<pre class="example">
// the variable 'value' below is the JavaScript native double value that is to be converted
(value).toExponential(6).replace(/(e(?:\+|-))([0-9])$/, '$10$2')</pre>

<p class="note">When data needs to be normalized, JSON-LD authors should
not use values that are going to undergo automatic conversion. This is due
to the lossy nature of <strong>xsd:double</strong> values.</p>

<p class="issue">Round-tripping data can be problematic if we mix and
match @coerce rules with JSON-native datatypes, like integers. Consider the 
following code example:</p>

<pre class="example">
var myObj = { "@context" : { 
                "number" : "http://example.com/vocab#number",
                "@coerce": {
                   "xsd:nonNegativeInteger": "number"
                }
              },
              "number" : 42 };

// Map the language-native object to JSON-LD
var jsonldText = jsonld.normalize(myObj);

// Convert the normalized object back to a JavaScript object
var myObj2 = jsonld.parse(jsonldText);</pre>

<p class="issue">At this point, myObj2 and myObj will have different
values for the "number" value. myObj will be the number 42, while
myObj2 will be the string "42". This type of data round-tripping
error can bite developers. We are currently wondering if having a
"coerce validation" phase in the parsing/normalization phases would be a 
good idea. It would prevent data round-tripping issues like the
one mentioned above.</p>

</div>

</div>



<div class="appendix section" id="markup-examples">

<!-- OddPage -->
<h2><span class="secno">A. </span>Markup Examples</h2>

<p>The JSON-LD markup examples below demonstrate how JSON-LD can be used to
express semantic data marked up in other languages such as RDFa, Microformats,
and Microdata. These sections are merely provided as proof that JSON-LD is
very flexible in what it can express across different Linked Data approaches.
</p>

<div id="rdfa" class="section">
<h3><span class="secno">A.1 </span>RDFa</h3>

<p>The following example describes three people with their respective names and
homepages.</p>

<pre class="example">
&lt;div <span class="diff">prefix="foaf: http://xmlns.com/foaf/0.1/"</span>&gt;
   &lt;ul&gt;
      &lt;li <span class="diff">typeof="foaf:Person"</span>&gt;
        &lt;a <span class="diff">rel="foaf:homepage" href="http://example.com/bob/" property="foaf:name" </span>&gt;Bob&lt;/a&gt;
      &lt;/li&gt;
      &lt;li <span class="diff">typeof="foaf:Person"</span>&gt;
        &lt;a <span class="diff">rel="foaf:homepage" href="http://example.com/eve/" property="foaf:name" </span>&gt;Eve&lt;/a&gt;
      &lt;/li&gt;
      &lt;li <span class="diff">typeof="foaf:Person"</span>&gt;
        &lt;a <span class="diff">rel="foaf:homepage" href="http://example.com/manu/" property="foaf:name" </span>&gt;Manu&lt;/a&gt;
      &lt;/li&gt;
   &lt;/ul&gt;
&lt;/div&gt;</pre>

<p>An example JSON-LD implementation is described below, however, there are
other ways to mark-up this information such that the context is not
repeated.</p>

<pre class="example">
[
 {
   "@": "_:bnode1",
   "a": "foaf:Person",
   "foaf:homepage": "http://example.com/bob/",
   "foaf:name": "Bob"
 },
 {
   "@": "_:bnode2",
   "a": "foaf:Person",
   "foaf:homepage": "http://example.com/eve/",
   "foaf:name": "Eve"
 },
 {
   "@": "_:bnode3",
   "a": "foaf:Person",
   "foaf:homepage": "http://example.com/manu/",
   "foaf:name": "Manu"
 }
]</pre>

</div>

<div id="microformats" class="section">
<h3><span class="secno">A.2 </span>Microformats</h3>

<p>The following example uses a simple Microformats hCard example to express
how the Microformat is represented in JSON-LD.</p>

<pre class="example">
&lt;div class="vcard"&gt;
 &lt;a class="url fn" href="http://tantek.com/"&gt;Tantek Çelik&lt;/a&gt;
&lt;/div&gt;</pre>

<p>The representation of the hCard expresses the Microformat terms in the
context and uses them directly for the <code>url</code> and <code>fn</code>
properties. Also note that the Microformat to JSON-LD processor has 
generated the proper URL type for <code>http://tantek.com</code>.</p>

<pre class="example">
{
  "@context": 
  {
    "vcard": "http://microformats.org/profile/hcard#vcard",
    "url": "http://microformats.org/profile/hcard#url",
    "fn": "http://microformats.org/profile/hcard#fn",
    "@coerce": { "xsd:anyURI": "url" }
  },
  "@": "_:bnode1",
  "a": "vcard",
  "url": "http://tantek.com/",
  "fn": "Tantek Çelik"
}</pre>

</div>

<div id="microdata" class="section">
<h3><span class="secno">A.3 </span>Microdata</h3>

<p>The Microdata example below expresses book information as a Microdata Work
item.
</p>

<pre class="example">
&lt;dl itemscope
    itemtype="http://purl.org/vocab/frbr/core#Work"
    itemid="http://purl.oreilly.com/works/45U8QJGZSQKDH8N"&gt;
 &lt;dt&gt;Title&lt;/dt&gt;
 &lt;dd&gt;&lt;cite itemprop="http://purl.org/dc/terms/title"&gt;Just a Geek&lt;/cite&gt;&lt;/dd&gt;
 &lt;dt&gt;By&lt;/dt&gt;
 &lt;dd&gt;&lt;span itemprop="http://purl.org/dc/terms/creator"&gt;Wil Wheaton&lt;/span&gt;&lt;/dd&gt;
 &lt;dt&gt;Format&lt;/dt&gt;
 &lt;dd itemprop="http://purl.org/vocab/frbr/core#realization"
     itemscope
     itemtype="http://purl.org/vocab/frbr/core#Expression"
     itemid="http://purl.oreilly.com/products/9780596007683.BOOK"&gt;
  &lt;link itemprop="http://purl.org/dc/terms/type" href="http://purl.oreilly.com/product-types/BOOK"&gt;
  Print
 &lt;/dd&gt;
 &lt;dd itemprop="http://purl.org/vocab/frbr/core#realization"
     itemscope
     itemtype="http://purl.org/vocab/frbr/core#Expression"
     itemid="http://purl.oreilly.com/products/9780596802189.EBOOK"&gt;
  &lt;link itemprop="http://purl.org/dc/terms/type" href="http://purl.oreilly.com/product-types/EBOOK"&gt;
  Ebook
 &lt;/dd&gt;
&lt;/dl&gt;</pre>

<p>Note that the JSON-LD representation of the Microdata information stays
true to the desires of the Microdata community to avoid contexts and
instead refer to items by their full IRI.</p>

<pre class="example">
[
  {
    "@": "http://purl.oreilly.com/works/45U8QJGZSQKDH8N",
    "a": "http://purl.org/vocab/frbr/core#Work",
    "http://purl.org/dc/terms/title": "Just a Geek",
    "http://purl.org/dc/terms/creator": "Whil Wheaton",
    "http://purl.org/vocab/frbr/core#realization": 
      ["http://purl.oreilly.com/products/9780596007683.BOOK", "http://purl.oreilly.com/products/9780596802189.EBOOK"]
  },
  {
    "@": "http://purl.oreilly.com/products/9780596007683.BOOK",
    "a": "http://purl.org/vocab/frbr/core#Expression",
    "http://purl.org/dc/terms/type": "http://purl.oreilly.com/product-types/BOOK"
  },
  {
    "@": "http://purl.oreilly.com/products/9780596802189.EBOOK",
    "a": "http://purl.org/vocab/frbr/core#Expression",
    "http://purl.org/dc/terms/type": "http://purl.oreilly.com/product-types/EBOOK"
  }
]</pre>
</div>

<div class="appendix section" id="mashing-up-vocabularies">
<h3><span class="secno">A.4 </span>Mashing Up Vocabularies</h3>

<p>Developers would also benefit by allowing other vocabularies to be used
automatically with their JSON API. There are over 200 
Vocabulary Documents that are available for use on the Web today. Some
of these vocabularies are:
</p>

<ul>
   <li>RDF - for describing information about objects on the semantic web.</li>
   <li>RDFS - for expressing things like labels and comments.</li>
   <li>XSD - for specifying basic types like strings, integers, dates and times.</li>
   <li>Dublin Core - for describing creative works.</li>
   <li>FOAF - for describing social networks.</li>
   <li>Calendar - for specifying events.</li>
   <li>SIOC - for describing discussions on blogs and websites.</li>
   <li>CCrel - for describing Creative Commons and other types of licenses.</li>
   <li>GEO - for describing geographic location.</li>
   <li>VCard - for describing organizations and people.</li>
   <li>DOAP - for describing projects.</li>
</ul>

<p>You can use these vocabularies in combination, like so:</p>

<pre class="example">
{
  "<span class="diff">rdf:type</span>": "<span class="diff">foaf:Person</span>",
  "<span class="diff">foaf:name</span>": "Manu Sporny",
  "<span class="diff">foaf:homepage</span>": "http://manu.sporny.org/",
  "<span class="diff">sioc:avatar</span>": "http://twitter.com/account/profile_image/manusporny"
}</pre>

<p>Developers can also specify their own Vocabulary documents by modifying the 
<a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a> in-line using the <code>@context</code> keyword, 
like so:</p>

<pre class="example">
{
  <span class="diff">"@context": { "myvocab": "http://example.org/myvocab#" }</span>,
  "a": "foaf:Person",
  "foaf:name": "Manu Sporny",
  "foaf:homepage": "http://manu.sporny.org/",
  "sioc:avatar": "http://twitter.com/account/profile_image/manusporny"<span class="diff">,
  "myvocab:personality": "friendly"</span>
}</pre>

<p>The <code>@context</code> keyword is used to change how the JSON-LD
processor evaluates key-value pairs. In this case, it was used to
map one string ('myvocab') to another string, which is interpreted as
a <a class="tref internalDFN" title="IRI" href="#dfn-iri">IRI</a>. In the example above, the <code>myvocab</code> string is replaced 
with "<code>http://example.org/myvocab#</code>" when it
is detected. In the example above, "<code>myvocab:personality</code>" would
expand to "<code>http://example.org/myvocab#personality</code>".</p>

<p>This mechanism is a short-hand for RDF, called a CURIE, and provides
developers an unambiguous way to map any JSON value to RDF.</p><p>

</p></div>

<div class="appendix section" id="acknowledgements">
<h3><span class="secno">A.5 </span>Acknowledgements</h3>

<p>The editors would like to thank Mark Birbeck, who provided a great deal of 
the initial push behind the JSON-LD work via his work on RDFj, 
Dave Longley, Dave Lehn and Mike Johnson who reviewed, provided feedback, and 
performed several implementations of the specification, and Ian Davis, who 
created RDF/JSON. Thanks also to Nathan Rixham, Bradley P. Allen,
Kingsley Idehen, Glenn McDonald, Alexandre Passant, Danny Ayers, Ted
Thibodeau Jr., Olivier Grisel, Niklas Lindström, Markus Lanthaler, and Richard 
Cyganiak for their input on the specification.</p>
</div>




</div><div id="respec-err" style="position: fixed; width: 350px; top: 10px; right: 10px; border: 3px double #f00; background: #fff" class="removeOnSave"><ul><li style="color: #c00">There appears to have been a problem fetching the style sheet; status=0</li></ul></div><div id="references" class="appendix section">
<!-- OddPage -->
<h2><span class="secno">B. </span>References</h2><div id="normative-references" class="section"><h3><span class="secno">B.1 </span>Normative references</h3><dl class="bibliography"><dt id="bib-BCP47">[BCP47]</dt><dd>A. Phillips, M. Davis. <a href="http://tools.ietf.org/rfc/bcp/bcp47.txt"><cite>Tags for Identifying Languages</cite></a> September 2009. IETF Best Current Practice. URL: <a href="http://tools.ietf.org/rfc/bcp/bcp47.txt">http://tools.ietf.org/rfc/bcp/bcp47.txt</a>
</dd><dt id="bib-RDF-API">[RDF-API]</dt><dd>Manu Sporny, Benjamin Adrian, Nathan Rixham; et al. <a href="http://www.w3.org/2010/02/rdfa/sources/rdf-api/"><cite>RDF API</cite></a> Latest. W3C Editor's Draft. URL: <a href="http://www.w3.org/2010/02/rdfa/sources/rdf-api/">http://www.w3.org/2010/02/rdfa/sources/rdf-api/</a>
</dd><dt id="bib-RDF-CONCEPTS">[RDF-CONCEPTS]</dt><dd>Graham Klyne; Jeremy J. Carroll. <a href="http://www.w3.org/TR/2004/REC-rdf-concepts-20040210"><cite>Resource Description Framework (RDF): Concepts and Abstract Syntax.</cite></a> 10 February 2004. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2004/REC-rdf-concepts-20040210">http://www.w3.org/TR/2004/REC-rdf-concepts-20040210</a> 
</dd><dt id="bib-RDF-INTERFACES">[RDF-INTERFACES]</dt><dd>Nathan Rixham, Manu Sporny, Benjamin Adrian; et al. <a href="http://www.w3.org/2010/02/rdfa/sources/rdf-interfaces/"><cite>RDF Interfaces</cite></a> Latest. W3C Editor's Draft. URL: <a href="http://www.w3.org/2010/02/rdfa/sources/rdf-interfaces/">http://www.w3.org/2010/02/rdfa/sources/rdf-interfaces/</a>
</dd><dt id="bib-RFC3987">[RFC3987]</dt><dd>M. Dürst; M. Suignard. <a href="http://www.ietf.org/rfc/rfc3987.txt"><cite>Internationalized Resource Identifiers (IRIs).</cite></a> January 2005. Internet RFC 3987. URL: <a href="http://www.ietf.org/rfc/rfc3987.txt">http://www.ietf.org/rfc/rfc3987.txt</a> 
</dd><dt id="bib-RFC4627">[RFC4627]</dt><dd>D. Crockford. <a href="http://www.ietf.org/rfc/rfc4627.txt"><cite>The application/json Media Type for JavaScript Object Notation (JSON)</cite></a> July 2006. Internet RFC 4627. URL: <a href="http://www.ietf.org/rfc/rfc4627.txt">http://www.ietf.org/rfc/rfc4627.txt</a>
</dd><dt id="bib-WEBIDL">[WEBIDL]</dt><dd>Cameron McCormack. <a href="http://www.w3.org/TR/2008/WD-WebIDL-20081219"><cite>Web IDL.</cite></a> 19 December 2008. W3C Working Draft. (Work in progress.) URL: <a href="http://www.w3.org/TR/2008/WD-WebIDL-20081219">http://www.w3.org/TR/2008/WD-WebIDL-20081219</a> 
</dd></dl></div><div id="informative-references" class="section"><h3><span class="secno">B.2 </span>Informative references</h3><dl class="bibliography"><dt id="bib-ECMA-262">[ECMA-262]</dt><dd><a href="http://www.ecma-international.org/publications/standards/Ecma-262.htm"><cite>ECMAScript Language Specification, Third Edition.</cite></a> December 1999. URL: <a href="http://www.ecma-international.org/publications/standards/Ecma-262.htm">http://www.ecma-international.org/publications/standards/Ecma-262.htm</a> 
</dd><dt id="bib-MICRODATA">[MICRODATA]</dt><dd>Ian Hickson; et al. <a href="http://www.w3.org/TR/microdata/"><cite>Microdata</cite></a> 04 March 2010. W3C Working Draft. URL: <a href="http://www.w3.org/TR/microdata/">http://www.w3.org/TR/microdata/</a> 
</dd><dt id="bib-MICROFORMATS">[MICROFORMATS]</dt><dd><a href="http://microformats.org"><cite>Microformats</cite></a>. URL: <a href="http://microformats.org">http://microformats.org</a> 
</dd><dt id="bib-RDFA-CORE">[RDFA-CORE]</dt><dd>Shane McCarron; et al. <a href="http://www.w3.org/TR/2011/WD-rdfa-core-20110331"><cite>RDFa Core 1.1: Syntax and processing rules for embedding RDF through attributes.</cite></a> 31 March 2011. W3C Working Draft. URL: <a href="http://www.w3.org/TR/2011/WD-rdfa-core-20110331">http://www.w3.org/TR/2011/WD-rdfa-core-20110331</a> 
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